DOUBLECLICK INC
S-4, 1999-10-21
ADVERTISING
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<PAGE>
    AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON OCTOBER 21, 1999

                                                   REGISTRATION NO. 333-[      ]
- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                            ------------------------

                                    FORM S-4
                             REGISTRATION STATEMENT

                        UNDER THE SECURITIES ACT OF 1933
                            ------------------------

                                DOUBLECLICK INC.

             (Exact Name of Registrant as Specified in its Charter)

<TABLE>
<S>                                       <C>                                       <C>
                DELAWARE                                    7319                                   13-3870996
               (State of                        (Primary Standard Industrial                    (I.R.S. Employer
             Incorporation)                         Classification Code)                     Identification Number)
</TABLE>

                         41 MADISON AVENUE, 32ND FLOOR
                            NEW YORK, NEW YORK 10010
                                 (212) 683-0001
              (Address, Including Zip Code, and Telephone Number,
       Including Area Code, of Registrant's Principal Executive Offices)
                            ------------------------

                               KEVIN J. O'CONNOR
                            CHIEF EXECUTIVE OFFICER
                                DOUBLECLICK INC.
                         41 MADISON AVENUE, 32ND FLOOR
                            NEW YORK, NEW YORK 10010
                                 (212) 683-0001
           (Name, Address, Including Zip Code, and Telephone Number,
                   Including Area Code, of Agent for Service)
                            ------------------------

                                   COPIES TO:

<TABLE>
<S>                                          <C>
         ALEXANDER D. LYNCH, ESQ.                     ROBERT L. LAWRENCE, ESQ.
          SCOTT L. KAUFMAN, ESQ.                        STEVEN E. COHEN, ESQ.
      BROBECK, PHLEGER & HARRISON LLP                    KANE KESSLER, P.C.
         1633 BROADWAY, 47TH FLOOR                   1350 AVENUE OF THE AMERICAS
         NEW YORK, NEW YORK 10019                     NEW YORK, NEW YORK 10019
              (212) 581-1600                               (212) 541-6222
</TABLE>

                            ------------------------

    APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC: At the
Effective Time of the Merger of a wholly-owned subsidiary of the Registrant with
and into Abacus Direct Corporation, which shall occur as soon as practicable
after the Effective Date of this Registration Statement, and the satisfaction or
waiver of all conditions to the closing of such Merger.

    If the securities being registered on this Form are being offered in
connection with the formation of a holding company and there is compliance with
General Instruction G, check the following box.  / /

    If this Form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act, please check the following box
and list the Securities Act registration statement number of the earlier
effective registration statement for the same offering.  / /

    If this Form is a post-effective amendment filed pursuant to Rule 462(c)
under the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
for the same offering.  / /

    If this Form is a post-effective amendment filed pursuant to Rule 462(d)
under the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
for the same offering.  / /

                        CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
         TITLE OF EACH CLASS                                 PROPOSED MAXIMUM       PROPOSED MAXIMUM
          OF SECURITIES TO                AMOUNT TO BE        OFFERING PRICE       AGGREGATE OFFERING         AMOUNT OF
            BE REGISTERED                 REGISTERED(1)          PER SHARE              PRICE(2)         REGISTRATION FEE(3)
<S>                                    <C>                  <C>                  <C>                     <C>
Common Stock, par value $.001 per
  share..............................      11,862,664               N/A            $1,311,954,121.88          $364,724
</TABLE>

(1) Based upon the maximum number of shares of the Registrant's common stock
    expected to be issued in connection with the merger, calculated as the
    product of (a) 11,297,775, the aggregate number of shares of Abacus Direct
    Corporation ("Abacus") common stock outstanding on October 1, 1999 and
    shares issuable pursuant to outstanding options prior to the date the merger
    is expected to be consummated and (b) an exchange ratio of 1.05 shares of
    the Registrant's common stock for each share of Abacus common stock.

(2) Estimated solely for purposes of calculating the registration fee required
    by Section 6(b) of the Securities Act of 1933, as amended, and calculated
    pursuant to Rule 457(f)(1) under the Securities Act. Pursuant to
    Rule 457(f)(1) under the Securities Act, the proposed maximum aggregate
    offering price of the Registrant's common stock was calculated in accordance
    with Rule 457(c) under the Securities Act as: (a) $116.125, the average of
    the high and low prices per share of Abacus common stock on October 18, 1999
    as reported on The Nasdaq National Market, multiplied by (b) 11,297,775, the
    aggregate number of shares of Abacus common stock outstanding on October 1,
    1999 and shares issuable pursuant to outstanding options prior to the date
    the merger is expected to be consummated.

(3) Pursuant to Rule 457(b), under the Securities Act, $151,728.09 of the
    registration fee is offset by the filing fee previously paid by the
    Registrant in connection with the filing of preliminary proxy materials on
    Schedule 14A on July 1, 1999.

                            ------------------------

    THE REGISTRANT HEREBY AMENDS THIS REGISTRATION STATEMENT ON SUCH DATE OR
DATES AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT SHALL
FILE A FURTHER AMENDMENT THAT SPECIFICALLY STATES THAT THIS REGISTRATION
STATEMENT SHALL THEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH SECTION 8(A) OF
THE SECURITIES ACT OF 1933 OR UNTIL THE REGISTRATION STATEMENT SHALL BECOME
EFFECTIVE ON SUCH DATE AS THE COMMISSION, ACTING PURSUANT TO SUCH SECTION 8(A),
MAY DETERMINE.

- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------
<PAGE>
                                     [LOGO]

                                                                October 22, 1999

Dear DoubleClick Stockholders:

    I am writing to you today about our proposed merger with Abacus Direct
Corporation. This merger will create a combined company to offer comprehensive
solutions for Internet advertising and direct marketing.

    In the merger, each share of Abacus common stock will be exchanged for 1.05
shares of DoubleClick common stock, par value $0.001 per share. We expect to
issue approximately 10.4 million shares of our common stock in the merger.
DoubleClick common stock is traded on the Nasdaq National Market under the
symbol "DCLK," and closed at $119.06 per share on October 19, 1999. The merger
is described more fully in this joint proxy statement/prospectus.

    You will be asked to vote upon the issuance of shares of DoubleClick common
stock pursuant to a merger agreement with Abacus, at a special meeting of
DoubleClick stockholders to be held on November 23, 1999 at 8:30 a.m., local
time, at 80 Fifth Avenue, 17th Floor, New York, New York 10011. The merger
cannot be consummated unless the holders of a majority of the shares of
DoubleClick common stock present in person or by proxy and entitled to vote at
the special meeting approve the issuance of these shares. Only stockholders who
hold shares of DoubleClick common stock at the close of business on October 1,
1999 will be entitled to vote at the special meeting.

    We are very excited by the opportunities we envision for the combined
company. YOUR BOARD OF DIRECTORS HAS DETERMINED THAT THE TERMS AND CONDITIONS OF
THE MERGER ARE FAIR TO YOU AND IN YOUR BEST INTERESTS, AND UNANIMOUSLY
RECOMMENDS THAT YOU APPROVE THE ISSUANCE OF THE SHARES OF DOUBLECLICK COMMON
STOCK IN CONNECTION WITH THE MERGER.

    This joint proxy statement/prospectus provides detailed information about
the two companies and the merger. Please give all of this information your
careful attention. IN PARTICULAR, YOU SHOULD CAREFULLY CONSIDER THE DISCUSSION
IN THE SECTION ENTITLED "RISK FACTORS" ON PAGE 15 OF THIS JOINT PROXY STATEMENT/
PROSPECTUS.

    YOUR VOTE IS VERY IMPORTANT REGARDLESS OF THE NUMBER OF SHARES YOU OWN.  To
vote your shares, you may use the enclosed proxy card, grant your proxy by
telephone or the Internet or attend the special stockholders meeting. To approve
the issuance of shares of DoubleClick common stock pursuant to the merger
agreement, you MUST vote "FOR" the proposal by following the instructions stated
on the enclosed proxy card. We urge you to vote FOR this proposal, a necessary
step in the merger of DoubleClick and Abacus.

                                          Sincerely,

                                          /s/ Kevin J. O'Connor

                                          Kevin J. O'Connor
                                          CHIEF EXECUTIVE OFFICER

NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES
COMMISSION HAS APPROVED OR DISAPPROVED OF THIS TRANSACTION OR THE DOUBLECLICK
COMMON STOCK TO BE ISSUED IN THE MERGER, OR DETERMINED IF THIS JOINT PROXY
STATEMENT/PROSPECTUS IS ACCURATE OR COMPLETE. ANY REPRESENTATION TO THE CONTRARY
IS A CRIMINAL OFFENSE.
    This joint proxy statement/prospectus is dated October 21, 1999, and was
first mailed to DoubleClick stockholders on or about October 22, 1999.
<PAGE>
                      REFERENCE TO ADDITIONAL INFORMATION

    This joint proxy statement/prospectus incorporates important business and
financial information about DoubleClick, Abacus and NetGravity from documents
that are not included in or delivered with this joint proxy
statement/prospectus. This information is available to you without charge upon
your written or oral request. You can obtain documents incorporated by reference
in this joint proxy statement/prospectus by requesting them in writing or by
telephone from DoubleClick, Abacus or NetGravity, as the case may be, at the
following addresses and telephone numbers:

<TABLE>
<S>                        <C>                        <C>
DoubleClick Inc.           Abacus:                    NetGravity, Inc.
Investor Relations         D.F. King & Co., Inc.      Investor Relations
41 Madison Avenue,         77 Water Street--20th      1900 S. Norfolk Street,
32nd Floor                 Floor                      Suite 150
New York, N.Y. 10010       New York, N.Y. 10005       San Mateo, CA 94403-1151
(212) 683-0001             800-769-6414               (650) 425-5960
</TABLE>

    IF YOU WOULD LIKE TO REQUEST DOCUMENTS, PLEASE DO SO BY NOVEMBER 16, 1999 IN
ORDER TO RECEIVE THEM BEFORE THE SPECIAL MEETINGS.

    See "Where you Can Find More Information" on page 89.
<PAGE>
                                DOUBLECLICK INC.
                         41 Madison Avenue, 32nd Floor
                               New York, NY 10010
                                 (212) 683-0001

                            ------------------------

                   NOTICE OF SPECIAL MEETING OF STOCKHOLDERS
                        TO BE HELD ON NOVEMBER 23, 1999

                            ------------------------

    We will hold a special meeting of stockholders of DoubleClick Inc. at
8:30 a.m., local time, on November 23, 1999 at 80 Fifth Avenue, 17th Floor, New
York, New York 10011:

        1. To consider and vote upon a proposal to approve the issuance of
    shares of common stock, par value $0.001 per share, of DoubleClick pursuant
    to a merger agreement, among DoubleClick, Abacus Direct Corporation and
    Atlanta Merger Corp., a wholly owned subsidiary of DoubleClick, under which
    Abacus will become a division of DoubleClick,

        2. To grant the DoubleClick Board of Directors discretionary authority
    to adjourn the special meeting to solicit additional votes for approval of
    the share issuance,

        3.  To consider and vote upon a proposal to approve the DoubleClick Inc.
    Employee Stock Purchase Plan, and

        4. To transact such other business as may properly come before the
    special meeting or any adjournment or postponement.

    Only DoubleClick stockholders of record at the close of business on
October 1, 1999 are entitled to notice of and to vote at the special meeting or
any adjournment or postponement.

    YOUR VOTE IS IMPORTANT REGARDLESS OF THE NUMBER OF SHARES YOU OWN. TO ASSURE
THAT YOUR SHARES ARE REPRESENTED AT THE SPECIAL MEETING, WE URGE YOU TO
COMPLETE, DATE AND SIGN THE ENCLOSED PROXY AND MAIL IT PROMPTLY IN THE
POSTAGE-PAID ENVELOPE PROVIDED, OR CALL THE TOLL-FREE TELEPHONE NUMBER OR USE
THE INTERNET BY FOLLOWING THE INSTRUCTIONS INCLUDED WITH YOUR PROXY CARD,
WHETHER OR NOT YOU PLAN TO ATTEND THE SPECIAL MEETING IN PERSON. YOU MAY REVOKE
YOUR PROXY IN THE MANNER DESCRIBED IN THIS JOINT PROXY STATEMENT/ PROSPECTUS AT
ANY TIME BEFORE IT HAS BEEN VOTED AT THE SPECIAL MEETING. YOU MAY VOTE IN PERSON
AT THE SPECIAL MEETING EVEN IF YOU HAVE RETURNED A PROXY.

                                          By Order of the Board of Directors

                                          /s/ Stephen R. Collins

                                          Stephen R. Collins
                                          SECRETARY

New York, New York
October 22, 1999
<PAGE>
                                     [LOGO]

                                                                October 22, 1999

Dear Abacus Stockholders:

    I am writing to you today about our proposed merger with DoubleClick Inc.
This merger will create a combined company to offer comprehensive solutions for
Internet advertising and direct marketing.

    In the merger, each share of Abacus common stock will be exchanged for 1.05
shares of DoubleClick common stock. DoubleClick expects to issue approximately
10.4 million shares of its common stock in the merger. DoubleClick common stock
is traded on the Nasdaq National Market under the trading symbol "DCLK," and
closed at $119.06 per share on October 19, 1999. The merger is described more
fully in this joint proxy statement/prospectus.

    You will be asked to vote upon the merger at a special meeting of Abacus
stockholders to be held on November 23, 1999 at 9:00 a.m., local time, at the
Rihga Royal Hotel, 151 West 54th Street, New York, New York 10019. The merger
cannot be consummated unless the holders of a majority of the shares of Abacus
common stock approve the merger. Only stockholders who hold shares of Abacus
common stock at the close of business on October 1, 1999 will be entitled to
vote at the special meeting.

    We are very excited by the opportunities we envision for the combined
company. YOUR BOARD OF DIRECTORS HAS DETERMINED THAT THE TERMS AND CONDITIONS OF
THE MERGER ARE FAIR TO YOU AND IN YOUR BEST INTERESTS, AND UNANIMOUSLY
RECOMMENDS THAT YOU APPROVE THE MERGER AGREEMENT AND THE MERGER.

    This joint proxy statement/prospectus provides detailed information about
the two companies and the merger. Please give all of this information your
careful attention. IN PARTICULAR, YOU SHOULD CAREFULLY CONSIDER THE DISCUSSION
IN THE SECTION ENTITLED "RISK FACTORS" ON PAGE 15 OF THIS JOINT PROXY STATEMENT/
PROSPECTUS.

    YOUR VOTE IS VERY IMPORTANT REGARDLESS OF THE NUMBER OF SHARES YOU OWN.  To
vote your shares, you may use the enclosed proxy card or attend the special
stockholders meeting. To approve the merger agreement, you MUST vote "FOR" the
proposal by following the instructions stated on the enclosed proxy card. If you
do not vote at all, it will, in effect, count as a vote against the merger. We
urge you to vote FOR this proposal, a necessary step in the merger of Abacus and
DoubleClick.

                                          Sincerely,

                                          /s/ M. Anthony White

                                          M. Anthony White
                                          CHAIRMAN OF THE BOARD AND CHIEF
                                          EXECUTIVE OFFICER

NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES
COMMISSION HAS APPROVED OR DISAPPROVED OF THIS TRANSACTION OR THE DOUBLECLICK
COMMON STOCK TO BE ISSUED IN THE MERGER, OR DETERMINED IF THIS JOINT PROXY
STATEMENT/PROSPECTUS IS ACCURATE OR COMPLETE. ANY REPRESENTATION TO THE CONTRARY
IS A CRIMINAL OFFENSE.
    This joint proxy statement/prospectus is dated October 21, 1999, and was
first mailed to Abacus stockholders on or about October 22, 1999.
<PAGE>
                           ABACUS DIRECT CORPORATION
                            11101 West 120th Street
                           Broomfield, Colorado 80021
                                 (303) 410-2800

                            ------------------------

                   NOTICE OF SPECIAL MEETING OF STOCKHOLDERS
                        TO BE HELD ON NOVEMBER 23, 1999

                            ------------------------

    We will hold a special meeting of stockholders of Abacus Direct Corporation
at 9:00 a.m., local time, on November 23, 1999 at the Rihga Royal Hotel, 151
West 54th Street, New York, New York 10019:

        1. To consider and vote upon a proposal to approve and adopt the merger
    agreement among DoubleClick Inc., Atlanta Merger Corp. and Abacus, under
    which each outstanding share of Abacus common stock will be converted into
    the right to receive 1.05 shares of DoubleClick common stock, and Abacus
    will become a division of DoubleClick,

        2. To grant the Abacus Board of Directors discretionary authority to
    adjourn the special meeting to solicit additional votes for approval of the
    merger agreement, and

        3. To transact such other business as may properly come before the
    special meeting or any adjournment or postponement.

    Only Abacus stockholders of record at the close of business on October 1,
1999 are entitled to notice of and to vote at the special meeting or any
adjournment or postponement.

    YOUR VOTE IS IMPORTANT REGARDLESS OF THE NUMBER OF SHARES YOU OWN. TO ASSURE
THAT YOUR SHARES ARE REPRESENTED AT THE SPECIAL MEETING, WE URGE YOU TO
COMPLETE, DATE AND SIGN THE ENCLOSED PROXY AND MAIL IT PROMPTLY IN THE
POSTAGE-PAID ENVELOPE PROVIDED, WHETHER OR NOT YOU PLAN TO ATTEND THE SPECIAL
MEETING IN PERSON. YOU MAY REVOKE YOUR PROXY IN THE MANNER DESCRIBED IN THIS
JOINT PROXY STATEMENT/PROSPECTUS AT ANY TIME BEFORE IT HAS BEEN VOTED AT THE
SPECIAL MEETING. YOU MAY VOTE IN PERSON AT THE SPECIAL MEETING EVEN IF YOU HAVE
RETURNED A PROXY.

                                          By Order of the Board of Directors

                                          /s/ Carlos E. Sala

                                          Carlos E. Sala
                                          SECRETARY

Broomfield, Colorado
October 22, 1999
<PAGE>
                               TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                PAGE
                                                              --------
<S>                                                           <C>

QUESTIONS AND ANSWERS ABOUT THE MERGER......................    iii

SUMMARY OF THE JOINT PROXY STATEMENT/PROSPECTUS.............      1

RISK FACTORS................................................     15

FORWARD-LOOKING STATEMENTS IN THIS JOINT PROXY STATEMENT/
  PROSPECTUS................................................     19

THE SPECIAL MEETINGS........................................     20
  General...................................................     20
  Date, Time and Place......................................     20
  Matters to be Considered at the Special Meetings..........     20
  Record Dates..............................................     21
  Voting of Proxies.........................................     21
  Votes Required............................................     22
  Quorum; Abstentions and Broker Non-Votes..................     22
  Solicitation of Proxies and Expenses......................     23
  Board Recommendations.....................................     23

THE MERGER..................................................     25
  Background of the Merger..................................     25
  Reasons for the Merger; Recommendations of Boards of
    Directors...............................................     29
  Opinions of Financial Advisors............................     33
  Interests of Abacus's Officers and Directors in the
    Merger..................................................     54
  Applicable Waiting Periods and Regulatory Approvals.......     56
  Material Federal Income Tax Considerations................     56
  Anticipated Accounting Treatment..........................     57
  No Appraisal Rights.......................................     58
  Delisting and Deregistration of Abacus's Common Stock
    Following the Merger....................................     58
  Listing of DoubleClick Common Stock to be Issued in the
    Merger..................................................     58
  Restrictions on Sale of Shares by Affiliates of
    DoubleClick and Abacus..................................     58
  Operations Following the Merger...........................     58

THE MERGER AGREEMENT AND RELATED AGREEMENTS.................     59
  The Merger................................................     59
  Effective Time............................................     59
  Conversion of Abacus Shares in the Merger.................     59
  Abacus Stock Option and Stock Incentive Plans.............     59
  No Fractional Shares......................................     60
  The Exchange Agent........................................     60
  Exchange of Abacus Stock Certificates for DoubleClick
    Stock Certificates......................................     60
  Distributions with Respect to Unexchanged Shares..........     60
  Representations and Warranties............................     61
  Abacus's Conduct of Business Before Completion of the
    Merger..................................................     62
  No Solicitation of Transactions...........................     64
  Director and Officer Indemnification and Insurance........     64
  Conditions to the Merger..................................     65
  Termination of the Merger Agreement.......................     66
  Payment of Fees and Expenses..............................     67
</TABLE>

                                       i
<PAGE>

<TABLE>
<CAPTION>
                                                                PAGE
                                                              --------
<S>                                                           <C>
  Extension, Waiver and Amendment of the Merger Agreement...     68
  Related Agreements........................................     68

PROPOSAL TO APPROVE DOUBLECLICK INC. EMPLOYEE STOCK PURCHASE
  PLAN                                                           72
  Share Reserve.............................................     72
  Administration............................................     73
  Offering Periods..........................................     73
  Eligibility...............................................     73
  Payroll Deductions........................................     73
  Purchase Price............................................     73
  Purchase Provisions.......................................     74
  Valuation.................................................     74
  Special Limitations.......................................     74
  Termination of Purchase Rights............................     74
  Stockholder Rights........................................     74
  Assignability.............................................     75
  Change in Control.........................................     75
  Amendment and Termination.................................     75
  Plan Benefits.............................................     75
  Federal Tax Consequences..................................     75
  Accounting Treatment......................................     76
  Stockholder Approval......................................     76

UNAUDITED PRO FORMA CONDENSED CONSOLIDATED FINANCIAL
  STATEMENTS                                                     77

COMPARISON OF RIGHTS OF HOLDERS OF ABACUS COMMON STOCK AND
  DOUBLECLICK COMMON STOCK..................................     85
  Classes of Common Stock of Abacus and DoubleClick.........     85
  Classified Board of Directors.............................     85
  Number of Directors.......................................     85
  Removal of Directors......................................     85
  Filling Vacancies on the Board of Directors...............     86
  Ability to Call Special Meetings..........................     86
  Advance Notice Provisions for Stockholder Nominations and
    Proposals...............................................     86
  Amendment of Certificate of Incorporation.................     87
  Amendment of Bylaws.......................................     88
  Indemnification of Directors and Officers.................     88

EXPERTS.....................................................     89

LEGAL MATTERS...............................................     89

WHERE YOU CAN FIND MORE INFORMATION.........................     89

INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE.............     90

APPENDICES
A--Agreement and Plan of Merger and Reorganization..........    A-1
B--Stock Option Agreement...................................    B-1
C--Form of Stockholder Agreement............................    C-1
D--Opinion of Goldman, Sachs & Co., Financial Advisor to
  DoubleClick...............................................    D-1
E--Opinion of BancBoston Robertson Stephens, Financial
  Advisor to Abacus.........................................    E-1
</TABLE>

                                       ii
<PAGE>
                     QUESTIONS AND ANSWERS ABOUT THE MERGER

Q: WHY ARE THE COMPANIES PROPOSING THE MERGER?

A: We believe that Abacus's strengths and capabilities complement DoubleClick's
    business. The merger is designed to create a company capable of offering Web
    publishers, advertisers and merchants effective and comprehensive Internet
    advertising and database marketing solutions.

Q: WHAT WILL ABACUS STOCKHOLDERS RECEIVE IN THE MERGER?

A: If the merger is completed, Abacus stockholders will receive 1.05 shares of
    DoubleClick common stock for each share of Abacus common stock they own.
    DoubleClick will not issue fractional shares of common stock. Instead of a
    fractional share, Abacus stockholders will receive cash based on the market
    price of DoubleClick common stock.

Q: DOUBLECLICK HAS ALSO ANNOUNCED THAT IT IS ACQUIRING NETGRAVITY, INC., HOW
    WILL THAT AFFECT ITS PROPOSED TRANSACTION WITH ABACUS?

A: On July 12, 1999, DoubleClick entered into an agreement to acquire
    NetGravity, Inc., a provider of solutions for online interactive marketing
    which includes online advertising and online direct marketing. Consummation
    of the NetGravity merger is NOT a condition to the consummation of
    DoubleClick's merger with Abacus. The proposed transaction with NetGravity
    is not expected to affect the consummation of the proposed transaction with
    Abacus.

Q: WHEN DO YOU EXPECT TO COMPLETE THE MERGER?

A: We are working to complete the merger in the fall of 1999. Because the merger
    is subject to governmental and other regulatory approvals, however, we
    cannot predict the exact timing.

Q: SHOULD ABACUS STOCKHOLDERS SEND IN THEIR STOCK CERTIFICATES NOW?

A: No. After we complete the merger, DoubleClick will send instructions to
    Abacus stockholders explaining how to exchange their shares of Abacus common
    stock for the appropriate number of shares of DoubleClick common stock.

Q: SHOULD DOUBLECLICK STOCKHOLDERS SEND IN THEIR STOCK CERTIFICATES?

A: No. DoubleClick stockholders will continue to own their shares of DoubleClick
    common stock after the merger and should continue to hold their stock
    certificates.

Q: HOW DO I VOTE?

A: Mail your signed proxy card in the enclosed return envelope as soon as
    possible so that your shares may be represented at the special stockholders
    meeting. You may also attend the meeting in person instead of submitting a
    proxy. If your shares are held in "street name" by your broker, your broker
    will vote your shares only if you provide instructions on how to vote. You
    should follow the directions provided by your broker regarding how to
    instruct your broker to vote your shares.

Q: CAN I CHANGE MY VOTE AFTER MAILING MY PROXY?

A: Yes. You may change your vote by delivering a signed notice of revocation or
    a later-dated, signed proxy card to the corporate secretary of DoubleClick
    or Abacus, as appropriate, before the appropriate stockholder meeting, or by
    attending the stockholder meeting and voting in person.

Q: ARE THERE RISKS I SHOULD CONSIDER IN DECIDING WHETHER TO VOTE FOR THE MERGER?

A: Yes. We have set out under the heading "Risk Factors" beginning on page 15 of
    this joint proxy statement/prospectus a number of risk factors that you
    should consider.

Q: WHO CAN I CALL WITH QUESTIONS?

A: If you are an Abacus stockholder with questions about the merger, please call
    Abacus's investor relations firm D.F. King & Co., Inc., 800-769-6414.

   If you are a DoubleClick stockholder with questions about the merger, please
    call DoubleClick's investor relations firm, Abernathy Macgregor Frank, at
    (212) 371-5999.

                                      iii
<PAGE>
                SUMMARY OF THE JOINT PROXY STATEMENT/PROSPECTUS

    THE FOLLOWING SUMMARY HIGHLIGHTS SELECTED INFORMATION FROM THIS JOINT PROXY
STATEMENT/PROSPECTUS AND MAY NOT CONTAIN ALL OF THE INFORMATION THAT IS
IMPORTANT TO YOU. YOU SHOULD CAREFULLY READ THIS ENTIRE JOINT PROXY
STATEMENT/PROSPECTUS, INCLUDING THE APPENDICES, AND THE OTHER DOCUMENTS WE REFER
TO FOR A MORE COMPLETE UNDERSTANDING OF THE MERGER.

THE COMPANIES

DOUBLECLICK INC.
41 Madison Avenue, 32nd Floor
New York, New York 10010
www.doubleclick.net
(212) 683-0001

    DoubleClick Inc. is a leading provider of comprehensive global Internet
advertising solutions for advertisers and Web publishers. DoubleClick delivers
Internet advertising to Web sites for advertisers and ad agencies in a targeted,
measurable and cost-effective manner through its DART-TM- technology. All of
DoubleClick's service offerings are powered by its DART technology, which offers
customers the ability to target, deliver, measure and analyze Internet marketing
campaigns on a real-time basis. DoubleClick has two principal service offerings:
the DoubleClick Network-TM- and DART Service. For Web publishers of the popular
Web sites that are in the DoubleClick Network, DoubleClick's in-house sales
force sells the advertising inventory available on those Web sites to
advertisers. Through the DART Service, DoubleClick serves as a service bureau
for clients of its DART for Publishers Services, consisting of Web publishers
that have their own sales staff, and also for clients of its Closed Loop
Marketing Solutions-TM- family of products, consisting of advertisers and their
ad agencies that wish to use the DART technology to deliver advertising to Web
sites of their choosing. DoubleClick operates in 17 countries around the world.

ABACUS DIRECT CORPORATION
11101 West 120th Street
Broomfield, Colorado 80021
www.abacus-direct.com
(303) 410-5100

    Abacus Direct Corporation is a leading provider of information products and
marketing research services to the direct marketing industry. Abacus has created
a comprehensive database of information on purchasing behavior by forming the
Abacus Alliance. The Abacus Alliance is a cooperative arrangement through which
direct marketers contribute their customers' purchasing histories to Abacus's
database in exchange for access to Abacus's information products and marketing
research services. This database, which includes purchasing data from over 1,300
catalog companies and other direct marketing companies, is a comprehensive
source of predictive information regarding consumer purchasing behavior. Abacus
uses this database and its advanced statistical modeling technology to provide
direct marketers information and analysis that allows them to increase response
rates and profits from their marketing campaigns.

THE MERGER (SEE PAGE 25)

    Abacus and DoubleClick have entered into a merger agreement that provides
for the merger of Abacus and a newly formed subsidiary of DoubleClick, which
following the merger will be merged into DoubleClick. Stockholders of Abacus
will become stockholders of DoubleClick following the merger, and each share of
Abacus common stock will be exchanged for 1.05 shares of DoubleClick common
stock. We urge you to read the merger agreement, which is attached as
APPENDIX A to this joint proxy statement/ prospectus, carefully and in its
entirety.

                                       1
<PAGE>
UNITED STATES FEDERAL INCOME TAX CONSEQUENCES OF THE MERGER (SEE PAGE 56)

    The merger has been structured as a tax-free reorganization for United
States federal income tax purposes. If the merger qualifies as a tax-free
reorganization, Abacus stockholders will not recognize gain or loss for United
States federal income tax purposes in the merger, except for taxes payable
because of cash they receive instead of fractional shares. It is a condition to
completion of the merger that we receive legal opinions from outside counsel
that the merger constitutes a tax-free reorganization within the meaning of the
Internal Revenue Code.

ABILITY TO SELL DOUBLECLICK STOCK AFTER THE MERGER (SEE PAGE 58)

    All shares of DoubleClick common stock that Abacus stockholders receive in
connection with the merger will be freely transferable unless the holder is
considered an "affiliate" of either DoubleClick or Abacus for purposes of the
Securities Act of 1933. Shares of DoubleClick common stock held by these
affiliates may be sold only under a registration statement or exemption under
the Securities Act.

NO DISSENTERS' OR APPRAISAL RIGHTS (SEE PAGE 58)

    Under Delaware law, stockholders of Abacus and DoubleClick are not entitled
to dissenters' or appraisal rights in the merger.

OPINIONS OF FINANCIAL ADVISORS (SEE PAGE 33)

    In deciding to approve the merger, the Abacus and DoubleClick boards of
directors considered opinions from each of their financial advisors.

    Goldman, Sachs & Co., DoubleClick's financial advisor, delivered its opinion
to the DoubleClick board of directors that, as of June 13, 1999, the share
exchange ratio was fair from a financial point of view to DoubleClick. The full
text of the written opinion of Goldman Sachs, dated June 13, 1999, is attached
as APPENDIX D to this joint proxy statement/prospectus. You should read this
opinion in its entirety.

    BancBoston Robertson Stephens, Abacus's financial advisor, delivered its
opinion to the Abacus board that, as of June 13, 1999, the share exchange ratio
was fair from a financial point of view to Abacus stockholders. The full text of
the written opinion of BancBoston Robertson Stephens, dated June 13, 1999, is
attached as APPENDIX E to this joint proxy statement/prospectus. You should read
this opinion in its entirety.

RECOMMENDATIONS OF THE BOARDS OF DIRECTORS (SEE PAGE 29)

    The Abacus and DoubleClick boards of directors have determined that the
terms and conditions of the merger are fair to, and in the best interests of,
their company's stockholders. The Abacus board unanimously recommends that
Abacus stockholders vote FOR approval of the merger agreement and the merger,
and the DoubleClick board unanimously recommends that DoubleClick stockholders
vote FOR issuing the shares of DoubleClick common stock in the merger.

STOCKHOLDER APPROVALS (SEE PAGE 22)

    ABACUS STOCKHOLDERS

    The holders of a majority of the outstanding shares of Abacus common stock
must approve the merger agreement and the merger. Abacus stockholders are
entitled to cast one vote per share of Abacus common stock owned at the close of
business on October 1, 1999. Under a stockholder agreement in the form attached
as APPENDIX B to this joint proxy statement/prospectus, Abacus stockholders
owning approximately 5% of Abacus's common stock, excluding any shares issuable
upon the exercise of options,

                                       2
<PAGE>
outstanding as of June 13, 1999 have agreed to vote all of their shares of
Abacus common stock for approval of the merger agreement and the merger.

    DOUBLECLICK STOCKHOLDERS

    The holders of a majority of the shares of DoubleClick common stock entitled
to vote and that are present or represented by proxy at the DoubleClick meeting
must approve the issuance of DoubleClick common stock in the merger. DoubleClick
stockholders are entitled to cast one vote per share of DoubleClick common stock
owned at the close of business on October 1, 1999.

INTERESTS OF ABACUS'S OFFICERS AND DIRECTORS IN THE MERGER (SEE PAGE 54)

    When considering the recommendation of the Abacus board, Abacus stockholders
should be aware that directors and officers of Abacus have the following
interests in the merger that are different from, or in addition to, those of
Abacus stockholders:

    - As of October 11, 1999, the executive officers and directors of Abacus
      owned stock options to purchase an aggregate of 984,902 shares of Abacus
      common stock, of which 638,447 are unvested. If the merger is completed,
      487,447 of the unvested options having a weighted exercise of $26.75 per
      share will become vested and immediately exercisable;

    - Abacus's senior executives are entitled to severance payments of
      approximately $3.9 million in the aggregate, under their employment
      agreements with Abacus if their employment is terminated upon Abacus's
      change of control, as is the case with the merger;

    - Upon completion of the merger, DoubleClick and Abacus will enter into
      employment agreements with the following officers of Abacus: M. Anthony
      White, Daniel C. Snyder, Carlos E. Sala, Christopher M. Dice and Brian M.
      Rainey;

    - DoubleClick has agreed to cause the surviving corporation in the merger to
      indemnify each present and former Abacus officer and director against
      liabilities arising out of his service as an officer or director. The
      surviving corporation in the merger will maintain officers' and directors'
      liability insurance to cover any of these liabilities for the next six
      years; and

    - DoubleClick intends to expand its board and to nominate M. Anthony White,
      the Chairman and Chief Executive Officer of Abacus, to be a director of
      DoubleClick.

As a result, Abacus's directors and officers may be more likely to vote to
approve the merger than Abacus stockholders generally.

CONDITIONS TO COMPLETION OF THE MERGER (SEE PAGE 65)

    We will complete the merger only if we satisfy or waive several conditions,
some of which are:

    - the merger agreement must be approved by Abacus's stockholders, and the
      issuance of DoubleClick common stock in the merger must be approved by
      DoubleClick's stockholders;

    - all necessary consents, approvals and authorizations from governmental
      entities must be obtained except where a failure to obtain the consent,
      approval or authorization could not be reasonably expected to have a
      material adverse effect on DoubleClick or Abacus;

    - no court of competent jurisdiction or governmental entity has issued or
      entered any order, writ, injunction or decree making the merger illegal or
      otherwise preventing its completion;

    - we must receive opinions from each of our tax counsels stating that the
      merger will qualify as a tax-free reorganization;

                                       3
<PAGE>
    - we must receive letters from each of our independent auditors regarding
      their concurrence with management as to the appropriateness of pooling of
      interest accounting for the merger;

    - no event, change, condition or effect that is or is reasonably likely to
      be materially adverse to Abacus and its subsidiaries, taken as a whole,
      occurs; and

    - Abacus's senior executives must have accepted employment by DoubleClick
      and entered into new employment and non-competition agreements.

If either of us waives any conditions, we will consider the facts and
circumstances at that time and determine whether completion of the merger
requires a resolicitation of proxies from stockholders.

RESTRICTIONS ON ALTERNATIVE TRANSACTIONS (SEE PAGE 64)

    The merger agreement prohibits Abacus from soliciting or participating in
discussions with third parties about transactions alternative to the merger.

TERMINATION OF THE MERGER AGREEMENT (SEE PAGE 66)

    We may mutually agree to terminate the merger agreement at any time before
the merger is completed. The merger agreement may also be terminated by either
of us for several other reasons, some of which are:

    - if the conditions to completion of the merger would not be satisfied
      because of either (A) a breach of an agreement in the merger agreement by
      the other party or (B) a breach of a representation or warranty in the
      merger agreement by the other party, if the breaching party does not take
      reasonable steps to cure the breach;

    - if the DoubleClick stockholders do not approve the issuance of DoubleClick
      common stock at the DoubleClick special meeting; or

    - if the Abacus stockholders do not approve the merger agreement and the
      merger at the Abacus special meeting.

    Furthermore, the merger agreement may be terminated by DoubleClick if any of
the following occurs:

    - Abacus's board withdraws or modifies in a manner adverse to DoubleClick
      its recommendation as to the merger agreement or the merger;

    - Abacus fails to comply with the nonsolicitation provisions of the merger
      agreement, which are discussed in more detail on page 64; or

    - Abacus's board recommends a transaction alternative to the merger, fails
      to recommend against a transaction alternative to the merger or fails to
      reconfirm its approval and recommendation of the merger.

TERMINATION FEE AND EXPENSES (SEE PAGE 67)

    Abacus may be required to pay DoubleClick a $30.0 million termination fee
and reimburse DoubleClick for its out-of-pocket expenses up to $2.5 million
following the termination of the merger, including a termination under the
circumstances described in the immediately preceding paragraph.

                                       4
<PAGE>
DOUBLECLICK REQUIRED ABACUS TO ENTER INTO A STOCK OPTION AGREEMENT WHICH MAY
DISCOURAGE PARTIES FROM SEEKING A STAKE IN ABACUS (SEE PAGE 68)

    In connection with the execution of the merger agreement, Abacus granted
DoubleClick a stock option to purchase up to 1,974,516 shares of Abacus common
stock at $93.25 per share. This share number represents approximately 19.99% of
the shares of Abacus common stock outstanding on June 13, 1999, or approximately
16.66% after issuance of the shares of Abacus common stock subject to the
option.

    DoubleClick may exercise the option only under circumstances in which the
termination fee is payable. Otherwise, the option will terminate and may not be
exercised by DoubleClick. The option limits DoubleClick's potential profit from
the sale of the shares underlying the option, together with the amount paid by
Abacus as a termination fee, at $50.0 million.

    DoubleClick required Abacus to grant the stock option as a prerequisite to
entering into the merger agreement. The stock option, the termination fee and
the nonsolicitation provisions of the merger agreement may discourage third
parties from seeking a significant stake in Abacus and are intended by
DoubleClick to increase the likelihood that the merger will be completed. We
encourage you to read the stock option agreement, which we have attached as
APPENDIX B to this joint proxy statement/prospectus.

ANTICIPATED ACCOUNTING TREATMENT OF THE MERGER (SEE PAGE 57)

    We expect the merger to qualify as a pooling of interests for financial
accounting purposes in accordance with generally accepted accounting principles.
It is a condition to completion of the merger that DoubleClick receive a letter
from its independent auditors regarding their concurrence with DoubleClick
management's conclusions as to the appropriateness of pooling-of-interests
accounting for the merger and that Abacus receive a letter from its independent
auditors regarding their concurrence with Abacus's management that Abacus is not
precluded from being a party to a merger accounted for as a pooling of
interests. DoubleClick may waive this condition. Under the pooling-of-interests
method of accounting, each of the parties' historical recorded assets and
liabilities will be carried forward to the combined company at their recorded
amounts. In addition, the operating results of the combined company will include
both parties' operating results for the entire fiscal year in which the merger
is completed, and the parties' historical reported operating results for prior
periods will be combined and restated as the operating results of the combined
company.

COMPLIANCE WITH ANTITRUST LAWS (SEE PAGE 56)

    The merger is subject to United States antitrust laws. We have made the
required filings with the Department of Justice and Federal Trade Commission. We
are not, however, permitted to complete the merger until the applicable waiting
period has expired or terminated. The applicable waiting period expired on
August 20, 1999. The Department of Justice and Federal Trade Commission, as well
as a state or private person, may challenge the merger at any time before or
after its completion.

RECENT DEVELOPMENTS

    On July 12, 1999, DoubleClick entered into an agreement to acquire
NetGravity, Inc. in a stock-for-stock merger. The following sets forth certain
pertinent information relating to the proposed transaction.

    BUSINESS OF NETGRAVITY

    NetGravity is a provider of solutions for online interactive marketing,
which includes online advertising and online direct marketing. NetGravity's
solutions are designed to help its customers increase their revenues by
automating online interactive marketing and by improving response rates through
better consumer targeting. NetGravity sells its solutions to each of the three
participants in the interactive marketing supply chain: e-commerce merchants,
advertising agencies and content publishers. NetGravity's

                                       5
<PAGE>
core product, AdServer, is a software solution targeted to large, sophisticated
e-commerce merchants and content publishers. AdServer manages the process of
placing advertisements, promotions and other offers on Web pages.

    TERMS OF THE NETGRAVITY MERGER

    Under the terms of the merger agreement with NetGravity, DoubleClick will
issue 0.28 shares of DoubleClick common stock for each outstanding share of
NetGravity common stock. In addition, all outstanding options to acquire shares
of NetGravity common stock will be assumed by DoubleClick and converted at the
same exchange ratio into options to purchase DoubleClick common stock. In the
acquisition, DoubleClick will exchange approximately 5 million shares of
DoubleClick common stock for all the issued and outstanding capital stock of
NetGravity. Following the merger, NetGravity will become a wholly owned
subsidiary of DoubleClick. DoubleClick and NetGravity expect the merger to be
accounted for as a "pooling of interests", and to qualify as a tax-free
reorganization. The merger is subject to a number of conditions, including
regulatory approval and approval by NetGravity's stockholders. DoubleClick
anticipates that the NetGravity merger will be consummated in the fall of 1999.

    EFFECT OF NETGRAVITY MERGER UPON ABACUS STOCKHOLDERS

    The primary effects of DoubleClick's merger with NetGravity on Abacus
stockholders will be dilution to their share ownership of DoubleClick,
consolidation of NetGravity losses by DoubleClick in its statements of
operations and increased costs to effect the integration into DoubleClick on a
prospective basis. The proposed acquisition of NetGravity will result in
dilution to DoubleClick stockholders, including Abacus stockholders who will
become DoubleClick stockholders as a result of the merger. Immediately after the
acquisition of Abacus, assuming the NetGravity merger has not yet been
completed, and further assuming the exercise of all outstanding DoubleClick and
Abacus options, Abacus stockholders would own approximately 21% of DoubleClick.
After the acquisition of Abacus, and assuming the NetGravity merger has been
completed, and further assuming the exercise of all outstanding DoubleClick,
NetGravity and Abacus options, Abacus stockholders will own approximately 19% of
DoubleClick. It is expected that the combined company's operating expenses will
increase following the NetGravity acquisition. This increase will result from
the integration of NetGravity into DoubleClick. In addition, the combined
company intends to expand its sales and marketing operations, fund greater
levels of product development and acquire complementary businesses, all of which
will increase operating expenses. If these expenses are not more than offset by
increased revenues over time, there may be an adverse impact on DoubleClick's
financial results. For additional information regarding the effect of the
NetGravity acquisition on the historical financial results of DoubleClick, see
"Unaudited Pro Forma Combined Financial Statements" on page 77.

                                       6
<PAGE>
                                DOUBLECLICK INC.
                SELECTED HISTORICAL CONSOLIDATED FINANCIAL DATA

                     (IN THOUSANDS, EXCEPT PER SHARE DATA)

    The following selected historical consolidated financial information should
be read in conjunction with DoubleClick's consolidated financial statements and
related notes and DoubleClick's "Management's Discussion and Analysis of
Financial Condition and Results of Operations", which we incorporate by
reference in this joint proxy statement/prospectus. The consolidated statement
of operations information for each of the two years ended December 31, 1998, and
for the period from January 23, 1996 (inception) through December 31, 1996 and
the consolidated balance sheet data at December 31, 1998 and 1997, are derived
from the consolidated financial statements of DoubleClick which have been
audited by PricewaterhouseCoopers LLP, independent accountants, and are
incorporated by reference in this joint proxy statement/prospectus. The selected
financial data for the six month periods ended June 30, 1999 and 1998 and as of
June 30, 1999 and 1998 have been derived from DoubleClick's unaudited financial
statements and in the opinion of DoubleClick's management include all
adjustments (consisting only of normal recurring adjustments) which are
necessary to present fairly the results of operations and financial position of
DoubleClick for those periods in accordance with generally accepted accounting
principles. Historical results are not necessarily indicative of the results to
be expected in the future.

<TABLE>
<CAPTION>
                                                                                                     FOR THE PERIOD FROM
                                                       SIX MONTHS ENDED           YEAR ENDED          JANUARY 23, 1996
                                                           JUNE 30,              DECEMBER 31,        (INCEPTION) THROUGH
                                                      -------------------   ----------------------      DECEMBER 31,
                                                        1999       1998       1998          1997            1996
                                                      --------   --------   --------      --------   -------------------
<S>                                                   <C>        <C>        <C>           <C>        <C>
CONSOLIDATED STATEMENT OF OPERATIONS DATA:
Revenues............................................  $ 53,079   $ 30,297   $ 80,188      $30,597          $ 6,514

Cost of revenues....................................    25,038     20,569     53,964       20,628            3,780
                                                      --------   --------   --------      -------          -------

Gross profit........................................    28,041      9,728     26,224        9,969            2,734

Operating expenses..................................    43,632     20,057     47,152       18,434            5,842
                                                      --------   --------   --------      -------          -------

Loss from operations................................   (15,591)   (10,329)   (20,928)      (8,465)          (3,108)
                                                      ========   ========   ========      =======          =======

Net loss............................................  $(12,536)  $ (9,101)  $(18,172)     $(8,356)         $(3,192)
                                                      ========   ========   ========      =======          =======

Basic and diluted net loss per share(1).............     (0.32)     (0.34)     (0.60)       (0.61)           (0.18)

Weighted average shares used in basic and diluted
  per share calculation.............................    39,435     27,101     30,440       13,718           18,118
</TABLE>

<TABLE>
<CAPTION>
                                                                AS OF JUNE 30,            AS OF DECEMBER 31,
                                                              -------------------   ------------------------------
                                                                1999       1998       1998       1997       1996
                                                              --------   --------   --------   --------   --------
<S>                                                           <C>        <C>        <C>        <C>        <C>

CONSOLIDATED BALANCE SHEET DATA:

Cash, cash equivalents and investments......................  $372,988   $56,566    $136,814   $ 8,546         --

Working capital (deficit)...................................   360,491    56,973     134,118     7,512     (3,038)

Total assets................................................   422,341    83,999     183,620    21,162      4,526

Convertible subordinated notes and other long term
  obligations...............................................   250,295       559         375       463         --

Stockholders' equity (deficit)..............................   137,165    63,207     148,338     9,400     (2,592)
</TABLE>

- ------------------------------

(1) Basic net loss per share is computed using the weighted average number of
    shares of common stock outstanding during the period, including the number
    of shares of common stock issued upon the conversion of convertible
    preferred stock, as of the date of conversion. Diluted net loss per share is
    based on the potential dilution that would occur on exercise or conversion
    of securities into common stock. Outstanding options to purchase shares of
    common stock that could potentially dilute basic earnings per share in the
    future were not included in the computation of diluted net loss per share
    because to do so would have had an antidilutive effect for the periods
    presented. Similarly, the computation of diluted net loss per share excludes
    the effect of shares issuable upon the conversion of convertible preferred
    stock since their inclusion would have had an antidilutive effect. As a
    result, the basic and diluted per share amounts are identical for all
    periods presented.

                                       7
<PAGE>
                           ABACUS DIRECT CORPORATION
                SELECTED HISTORICAL CONSOLIDATED FINANCIAL DATA
                     (IN THOUSANDS, EXCEPT PER SHARE DATA)

    The following selected historical consolidated financial data should be read
in conjunction with Abacus's consolidated financial statements and related notes
and Abacus's "Management's Discussion and Analysis of Financial Condition and
Results of Operations", which we incorporate by reference in this joint proxy
statement/prospectus. The consolidated statement of operations data for each of
the three years ended December 31, 1998, and the consolidated balance sheet data
at December 31, 1998 and 1997, are derived from the consolidated financial
statements of Abacus which have been audited by PricewaterhouseCoopers LLP,
independent accountants, and are incorporated by reference in this joint proxy
statement/prospectus. The statement of operations data for the years ended
December 31, 1995 and 1994, and the balance sheet data at December 31, 1996,
1995 and 1994, are derived from financial statements of Abacus which have been
audited by PricewaterhouseCoopers LLP, are not included or incorporated by
reference in this document. The selected financial data for the six month
periods ended June 30, 1999 and 1998 and as of June 30, 1999 and 1998 have been
derived from Abacus's unaudited financial statements and in the opinion of
Abacus's management include all adjustments (consisting only of normal recurring
adjustments) which are necessary to present fairly the results of operations and
financial position of Abacus for those periods in accordance with generally
accepted accounting principles. Historical results are not necessarily
indicative of the results to be expected in the future.

<TABLE>
<CAPTION>
                                          SIX MONTHS ENDED
                                              JUNE 30,                       YEAR ENDED DECEMBER 31,
                                         -------------------   ----------------------------------------------------
<S>                                      <C>        <C>        <C>        <C>        <C>        <C>        <C>
                                          1999       1998       1998       1997       1996       1995       1994
                                         -------    -------    -------    -------    -------     ------     ------
CONSOLIDATED STATEMENT OF OPERATIONS DATA:
Revenues...............................  $25,968    $18,449    $46,979    $30,971    $17,532     $9,331     $6,451
Cost of revenue........................    6,463      4,227      9,581      5,942      3,751      1,886      1,475
                                         -------    -------    -------    -------    -------     ------     ------
Gross profit...........................   19,505     14,222     37,398     25,029     13,781      7,445      4,976
Operating expenses.....................   12,166      9,031     19,607(1)  13,520      7,411      4,271      2,581
                                         -------    -------    -------    -------    -------     ------     ------
Income from operations.................    7,339      5,191     17,791     11,509      6,370      3,174      2,395
                                         =======    =======    =======    =======    =======     ======     ======
Net income.............................  $ 4,577    $ 3,490    $11,426    $ 7,497    $ 3,865     $2,426     $2,012
                                         =======    =======    =======    =======    =======     ======     ======
  Basic net income per share...........  $  0.46    $  0.36    $  1.17    $  0.78    $  0.43     $ 0.27     $ 0.57
  Diluted net income per share.........  $  0.44    $  0.34    $  1.12    $  0.74    $  0.40     $ 0.27     $ 0.23
  Weighted average shares used in basic
    per share calculation..............    9,878      9,692      9,727      9,546      9,094      9,079      3,513
  Weighted average shares used in
    diluted per share calculation......   10,475     10,202     10,216     10,058      9,614      9,120      8,743
</TABLE>

<TABLE>
<CAPTION>
                                             AS OF JUNE 30,                       AS OF DECEMBER 31,
                                           -------------------   ----------------------------------------------------
                                             1999       1998       1998       1997       1996       1995       1994
                                           --------   --------   --------   --------   --------   --------   --------
<S>                                        <C>        <C>        <C>        <C>        <C>        <C>        <C>
CONSOLIDATED BALANCE SHEET DATA:
  Cash and cash equivalents..............  $23,563    $13,496    $24,263    $10,490     $5,924     $1,345     $1,856
  Working capital........................   35,965     19,867     32,358     16,127      8,218      2,424      2,386
  Total assets...........................   48,981     26,789     43,320     22,592     12,064      5,050      4,244
  Long-term obligations..................      447          8        613         15         29      2,301      2,814
  Stockholders' equity (deficit).........   42,778     23,567     36,304     19,177     10,012      1,190     (1,233)
</TABLE>

                                       8
<PAGE>
              SELECTED UNAUDITED PRO FORMA COMBINED FINANCIAL DATA

    In the table below, we provide you selected unaudited pro forma combined
financial data to give effect to the proposed merger of DoubleClick and Abacus
as if the merger had been completed on January 1, 1996 for statement of
operations purposes and on June 30, 1999 for balance sheet purposes. This
selected unaudited pro forma combined financial data should be read in
conjunction with the separate historical financial statements and accompanying
notes of DoubleClick and of Abacus, which are incorporated by reference in this
joint proxy statement/prospectus. It is also important that you read the
DoubleClick 1998 Annual Report on Form 10-K, as amended by Annual Report on Form
10K/A which we incorporate by reference. See "Where You Can Find More
Information." You should not rely on the selected unaudited pro forma combined
financial information as an indication of the results of operations or financial
position that would have been achieved if the transaction with Abacus had taken
place earlier or of the results of operations or financial position of
DoubleClick after the completion of these transactions.

    The selected unaudited pro forma combined financial information gives effect
to the proposed merger of DoubleClick and Abacus on a pooling of interests
basis. The DoubleClick and Abacus unaudited pro forma combined balance sheet
data assume that the merger of DoubleClick and Abacus took place on June 30,
1999, and combines the DoubleClick historical consolidated balance sheet with
Abacus's historical consolidated balance sheet as of this date. The DoubleClick
and Abacus unaudited pro forma combined statements of operations data assume
that the merger of DoubleClick and Abacus took place as of the beginning of the
periods presented and combine DoubleClick's historical consolidated statements
of operations data for the years ended December 31, 1998 and 1997 and for the
period from January 23, 1996 (inception) through December 31, 1996, and for the
six months ended June 30, 1999 and 1998 with Abacus's historical consolidated
statements of operations data for the years ended December 31, 1998, 1997 and
1996, and for the six months ended June 30, 1999 and 1998. This presentation is
consistent with the periods expected to be combined after the date of the
closing of the merger.

    On July 12, 1999, DoubleClick entered into an agreement to merge with
NetGravity, Inc. in a transaction expected to be accounted for as a pooling of
interests. See "Recent Developments." The DoubleClick, Abacus and NetGravity
unaudited combined financial data are based on the historical consolidated
financial statements and related notes of DoubleClick, Abacus and NetGravity.
This presentation is on the same basis as the DoubleClick and Abacus unaudited
pro forma combined financial data described above and is consistent with the
years expected to be combined after the closing dates for the mergers with
Abacus and NetGravity.

    The selected unaudited pro forma combined financial data are presented for
illustrative purposes only and are not necessarily indicative of the combined
financial position or results of operations of future periods or the results
that actually would have been realized had the entities been a single entity
during these periods. Note also that the consummation of the merger of
DoubleClick and NetGravity is NOT a condition to the merger of DoubleClick and
Abacus. The selected unaudited pro forma combined financial data as of June 30,
1999 and for each of the periods ended December 31, 1998, 1997, and 1996, and
for the six months ended June 30, 1999 and 1998, are derived from the unaudited
pro forma condensed combined financial statements included elsewhere in this
joint proxy statement/prospectus and should be read in conjunction with those
statements and the related notes. See "Unaudited Pro Forma Condensed Combined
Financial Statements."

                                       9
<PAGE>
              SELECTED UNAUDITED PRO FORMA COMBINED FINANCIAL DATA

                 DOUBLECLICK INC. AND ABACUS DIRECT CORPORATION

<TABLE>
<CAPTION>
                                                  SIX MONTHS ENDED                YEAR ENDED
                                                      JUNE 30,                   DECEMBER 31,
                                               ----------------------   ------------------------------
                                                 1999          1998       1998       1997     1996(1)
                                               --------      --------   --------   --------   --------
                                                      (IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)
<S>                                            <C>           <C>        <C>        <C>        <C>
UNAUDITED PRO FORMA COMBINED
  STATEMENT OF OPERATIONS DATA:
Revenues.....................................  $79,047       $48,746    $127,167   $61,568    $24,046
Gross profit.................................   47,546        23,950      63,622    34,998     16,515
Total operating expenses.....................   55,798        29,088      66,759    31,954     13,253
Net income (loss) applicable to common
  stockholders...............................  $(7,959)      $(5,611)   $ (6,746)  $  (859)   $   673
Net income (loss) per share--basic...........  $ (0.16)      $ (0.15)   $  (0.17)  $ (0.04)   $  0.02
Net income (loss) per share--diluted.........  $ (0.16)      $ (0.15)   $  (0.17)  $ (0.04)   $  0.02
Weighted Average Shares used in per share
  calculation--basic.........................   49,807        37,278      40,654    23,740     27,667
Weighted Average Shares used in per share
  calculation--diluted.......................   49,807        37,278      40,654    23,740     28,213
</TABLE>

<TABLE>
<CAPTION>
                                                              JUNE 30, 1999
                                                              --------------
                                                              (IN THOUSANDS)
<S>                                                           <C>
UNAUDITED PRO FORMA COMBINED BALANCE SHEET DATA:
Cash, cash equivalents, and short-term investments..........     $396,551
Working capital.............................................      380,456
Total assets................................................      471,322
Convertible subordinated notes and other long term
  obligations...............................................      250,742
Stockholders' equity........................................      163,943
</TABLE>

- ------------------------

(1) Period from January 23, 1996 (inception) through December 31, 1996 regarding
    DoubleClick.

                                       10
<PAGE>
              SELECTED UNAUDITED PRO FORMA COMBINED FINANCIAL DATA

                  DOUBLECLICK INC., ABACUS DIRECT CORPORATION

                              AND NETGRAVITY, INC.

<TABLE>
<CAPTION>
                                               SIX MONTHS ENDED               YEAR ENDED
                                                   JUNE 30,                  DECEMBER 31,
                                              -------------------   ------------------------------
                                                1999       1998       1998       1997     1996(1)
                                              --------   --------   --------   --------   --------
                                                    (IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)
<S>                                           <C>        <C>        <C>        <C>        <C>
UNAUDITED PRO FORMA COMBINED STATEMENT OF
  OPERATIONS DATA:
Revenues....................................  $ 89,268   $ 53,081   $138,724   $ 67,926   $25,985
Gross profit................................    52,971     26,000     69,951     38,784    17,752
Total operating expenses....................    68,690     37,004     84,921     42,612    19,171
Net loss applicable to common
  stockholders..............................  $(13,811)  $(11,421)  $(18,039)  $ (7,741)   (3,954)
Net loss per share--basic and diluted.......  $  (0.25)  $  (0.30)  $  (0.42)  $  (0.32)  $ (0.14)
Weighted Average Shares used in per share
  calculation--basic and diluted............    54,167     38,420     43,124     24,524    28,258
</TABLE>

<TABLE>
<CAPTION>
                                                              JUNE 30, 1999
                                                              --------------
                                                              (IN THOUSANDS)
<S>                                                           <C>
UNAUDITED PRO FORMA COMBINED BALANCE SHEET DATA:
Cash, cash equivalents, and short-term investments..........      $521,594
Working capital.............................................       493,205
Total assets................................................       615,030
Convertible subordinated notes and other long term
  obligations...............................................       250,742
Stockholders' equity........................................       284,217
</TABLE>

- ------------------------

(1) Period from January 23, 1996 (inception) through December 31, 1996 regarding
    DoubleClick.

                                       11
<PAGE>
                           COMPARATIVE PER SHARE DATA

    The following tables reflect (a) the historical net loss and book value per
share of DoubleClick common stock, the historical net income and book value per
share of Abacus common stock, and the historical net loss and book value per
share of NetGravity common stock in comparison with the unaudited pro forma net
loss and book value per share after giving effect to the proposed merger of
DoubleClick with Abacus and DoubleClick and Abacus with NetGravity on a "pooling
of interests" basis and (b) the equivalent historical net loss and book value
per share attributable to 1.05 shares of DoubleClick common stock that will be
received for each share of Abacus common stock in the merger and 0.28 shares of
DoubleClick common stock that will be received for each share of NetGravity
common stock in that merger. The information presented in the following tables
should be read in conjunction with the unaudited pro forma condensed combined
financial statements included in this joint proxy statement/ prospectus and the
historical consolidated financial statements and related notes of DoubleClick,
Abacus and NetGravity which are incorporated by reference in this joint proxy
statement/prospectus.

<TABLE>
<CAPTION>
                                                           SIX MONTHS
                                                              ENDED                    YEAR ENDED
                                                            JUNE 30,                  DECEMBER 31,
                                                       -------------------   ------------------------------
                                                         1999       1998       1998       1997     1996(4)
                                                       --------   --------   --------   --------   --------
<S>                                                    <C>        <C>        <C>        <C>        <C>
DOUBLECLICK HISTORICAL PER COMMON SHARE:
Net loss per common share--basic and diluted(2)......   $(0.32)    $(0.34)    $(0.60)    $(0.61)    $(0.18)
Book value per share(1)..............................   $ 3.45                $ 3.79

ABACUS HISTORICAL PER COMMON SHARE:
Net income per common share--basic(2)................   $ 0.46     $ 0.36     $ 1.17     $ 0.78     $ 0.43
Net income per common share--diluted(2)..............   $ 0.44     $ 0.34     $ 1.12     $ 0.74     $ 0.40
Book value per share(1)..............................   $ 4.32                $ 3.68

DOUBLECLICK AND ABACUS PRO FORMA COMBINED PER COMMON
  SHARE:
Net income (loss) per DoubleClick share--basic(2)....   $(0.16)    $(0.15)    $(0.17)    $(0.04)    $ 0.02
Net income (loss) per DoubleClick
  share--diluted(2)..................................    (0.16)     (0.15)     (0.17)     (0.04)      0.02
Net income (loss) per equivalent Abacus
  share--basic(3)....................................    (0.17)     (0.16)     (0.17)     (0.04)      0.03
Net income (loss) per equivalent Abacus
  share--diluted(3)..................................    (0.17)     (0.16)     (0.17)     (0.04)      0.03
Book value per Doubleclick share(1)..................   $ 3.27                $ 3.41
Book value per equivalent Abacus share(3)............   $ 3.43                $ 3.58
</TABLE>

                                       12
<PAGE>

<TABLE>
<CAPTION>
                                                           SIX MONTHS
                                                              ENDED                    YEAR ENDED
                                                            JUNE 30,                  DECEMBER 31,
                                                       -------------------   ------------------------------
                                                         1999       1998       1998       1997     1996(4)
                                                       --------   --------   --------   --------   --------
<S>                                                    <C>        <C>        <C>        <C>        <C>
NETGRAVITY HISTORICAL PER COMMON SHARE:
Net loss per common share--basic and diluted(2)......    (0.38)     (1.42)     (1.28)     (2.46)     (2.19)
Book value per share(1)..............................     7.38                  1.63

DOUBLECLICK, ABACUS, AND NETGRAVITY PRO FORMA
  COMBINED PER COMMON SHARE:
Net loss per DoubleClick share--basic(2).............   $(0.25)     (0.30)     (0.42)     (0.32)     (0.14)
Net loss per DoubleClick share--diluted(2)...........   $(0.25)     (0.30)     (0.42)     (0.32)     (0.14)
Net loss per equivalent Abacus share--basic(3).......   $(0.27)     (0.31)     (0.44)     (0.33)     (0.15)
Net loss per equivalent Abacus share--diluted(3).....   $(0.27)     (0.31)     (0.44)     (0.33)     (0.15)
Book value per DoubleClick share(1)..................   $ 5.16                $ 3.38
Book value per equivalent Abacus share(3)............   $ 5.41                $ 3.55
</TABLE>

- ------------------------

(1) The historical book value per share is computed by dividing stockholders'
    equity by the number of shares of common stock outstanding at June 30, 1999.
    The pro forma combined book value per share is computed by dividing pro
    forma stockholders' equity by the pro forma number of shares of DoubleClick
    common stock outstanding as of June 30, 1999 assuming the merger had
    occurred as of that date.

(2) Basic net income (loss) per share is computed using the weighted average
    number of shares of common stock outstanding during the period. Diluted net
    income (loss) per share is computed using the weighted average number of
    common and common equivalent shares outstanding during the period. Common
    equivalent shares consist of the incremental common shares issuable upon
    conversion of the convertible preferred stock (using the if-converted
    method) and shares issuable upon the exercise of stock options (using the
    treasury stock method). Common equivalent shares are excluded from the
    computations if their effect is antidilutive.

(3) The equivalent pro forma combined per Abacus share is calculated by
    multiplying the pro forma combined share amounts by the exchange ratio of
    1.05 shares of DoubleClick common stock for each share of Abacus common
    stock.

(4) Period from January 23, 1996 (inception) through December 31, 1996 regarding
    DoubleClick.

                                       13
<PAGE>
                            MARKET PRICE INFORMATION

DOUBLECLICK MARKET PRICE DATA

    DoubleClick's common stock has traded on the Nasdaq National Market under
the symbol "DCLK" since February 20, 1998. The following table sets forth the
range of high and low sales prices reported on the Nasdaq National Market for
DoubleClick common stock for the periods indicated, adjusted to reflect a
two-for-one stock split effected in the form of a dividend which became
effective on April 5, 1999.

<TABLE>
<CAPTION>
                                                               HIGH       LOW
                                                             --------   --------
<S>                                                          <C>        <C>
FISCAL 1998
  First Quarter (since February 20, 1998)..................  $ 18.50     $13.81
  Second Quarter...........................................    24.88      15.44
  Third Quarter............................................    38.56       9.09
  Fourth Quarter...........................................    29.00       6.75
FISCAL 1999
  First Quarter............................................  $100.00     $22.00
  Second Quarter...........................................   176.00      67.50
  Third Quarter............................................   125.25      60.50
  Fourth Quarter (through October 19, 1999)................   138.18     109.75
</TABLE>

ABACUS MARKET PRICE DATA

    Abacus's common stock has traded on the Nasdaq National Market under the
symbol "ABDR" since September 27, 1996. The following table sets forth the range
of high and low sales prices reported on the Nasdaq National Market for Abacus
common stock for the periods indicated.

<TABLE>
<CAPTION>
                                                                HIGH       LOW
                                                              --------   --------
<S>                                                           <C>        <C>
FISCAL 1997
  First Quarter.............................................   $30.25     $18.00
  Second Quarter............................................    33.25      17.00
  Third Quarter.............................................    34.25      26.50
  Fourth Quarter............................................    44.25      31.38
FISCAL 1998
  First Quarter.............................................   $52.25     $32.88
  Second Quarter............................................    58.38      44.00
  Third Quarter.............................................    57.50      38.50
  Fourth Quarter............................................    59.75      33.75
FISCAL 1999
  First Quarter.............................................   $84.75     $41.00
  Second Quarter............................................    99.00      60.00
  Third Quarter.............................................   128.56      60.62
  Fourth Quarter (through October 19, 1999).................   140.50     111.25
</TABLE>

RECENT CLOSING PRICES

    As of June 11, 1999, the last trading day before announcement of the
proposed merger, the closing price per share on the Nasdaq National Market of
DoubleClick common stock was $88.81 and of Abacus common stock was $74.56. On
October 19, 1999, the latest practicable trading day before the printing of this
joint proxy statement/prospectus, the closing price per share of DoubleClick
common stock was $119.06 and of Abacus was $121.06.

    Because the market price of DoubleClick common stock is subject to
fluctuation, the market value of the shares of DoubleClick common stock that
holders of Abacus common stock will receive in the merger may increase or
decrease prior to and following the merger. WE URGE STOCKHOLDERS TO OBTAIN
CURRENT MARKET QUOTATIONS FOR DOUBLECLICK COMMON STOCK AND ABACUS COMMON STOCK.
WE CANNOT ASSURE YOU AS TO THE FUTURE PRICES OR MARKETS FOR DOUBLECLICK COMMON
STOCK OR ABACUS COMMON STOCK.

                                       14
<PAGE>
                                  RISK FACTORS

    BY VOTING IN FAVOR OF THE MERGER, ABACUS STOCKHOLDERS WILL BE CHOOSING TO
INVEST IN DOUBLECLICK COMMON STOCK. AN INVESTMENT IN DOUBLECLICK COMMON STOCK
INVOLVES A HIGH DEGREE OF RISK. IN ADDITION TO THE OTHER INFORMATION CONTAINED
IN OR INCORPORATED BY REFERENCE INTO THIS JOINT PROXY STATEMENT/PROSPECTUS, YOU
SHOULD CAREFULLY CONSIDER THE FOLLOWING RISK FACTORS IN DECIDING WHETHER TO VOTE
FOR THE MERGER. IF ANY OF THE FOLLOWING RISKS ACTUALLY OCCUR, THE BUSINESS AND
PROSPECTS OF ABACUS OR DOUBLECLICK MAY BE SERIOUSLY HARMED. IN THIS CASE, THE
TRADING PRICE OF DOUBLECLICK COMMON STOCK MAY DECLINE, AND YOU MAY LOSE ALL OR
PART OF YOUR INVESTMENT.

                          RISKS RELATED TO THE MERGER

ABACUS STOCKHOLDERS WILL RECEIVE A FIXED NUMBER OF SHARES OF DOUBLECLICK COMMON
STOCK AND AS A RESULT, THEY WILL BEAR ALL THE MARKET RISK OF A DECREASE OF THE
VALUE OF DOUBLECLICK SHARES ISSUED IN THE MERGER.

    Upon the merger's completion, each share of Abacus common stock will be
exchanged for 1.05 shares of DoubleClick common stock. There will be no
adjustment for changes in the market price of either Abacus common stock or
DoubleClick common stock. In addition, neither Abacus nor DoubleClick may
terminate the merger agreement or "walk away" from the merger or resolicit the
vote of its stockholders solely because of changes in the market price of
DoubleClick common stock. Accordingly, the specific dollar value of DoubleClick
common stock that Abacus stockholders will receive upon the merger's completion
will depend on the market value of DoubleClick common stock when the merger is
completed and may decrease from the date you submit your proxy. The share price
of DoubleClick common stock is by nature subject to the general price
fluctuations in the market for publicly traded equity securities and has
experienced significant volatility. We urge you to obtain recent market
quotations for DoubleClick common stock and Abacus common stock. DoubleClick
cannot predict or give any assurances as to the market price of DoubleClick
common stock at any time before or after the completion of the merger.

IF WE DO NOT SUCCESSFULLY INTEGRATE ABACUS'S OPERATIONS AND PERSONNEL OR
EFFECTIVELY MANAGE THE COMBINED COMPANY, WE MAY NOT ACHIEVE THE BENEFITS OF THE
MERGER AND MAY LOSE KEY PERSONNEL AND CUSTOMERS.

    We entered into the merger agreement with the expectation that the merger
will result in significant benefits. Achieving the benefits of the merger
depends on the timely, efficient and successful execution of a number of
post-merger events, including integrating the operations and personnel of the
two companies. We will need to overcome significant issues, however, in order to
realize any benefits or synergies from the merger. The successful execution of
these post-merger events will involve considerable risk and may not be
successful. Abacus is a provider of information products and marketing research
services to the direct marketing industry. DoubleClick is a provider of
advertising solutions for advertisers and Web publishers, and has virtually no
experience in Abacus's business. Furthermore, Abacus's principal offices are
located in Broomfield, Colorado, while DoubleClick's principal offices are
located in New York, New York. There are currently no plans to relocate either
of these principal offices. In order for the merger to be successful, we must
successfully integrate Abacus's operations and personnel with DoubleClick's
operations and personnel. The failure of DoubleClick to complete the integration
successfully could result in the loss of key personnel and customers.

IF WE FAIL TO SUCCESSFULLY CROSS-MARKET OUR PRODUCTS OR DEVELOP NEW PRODUCTS, WE
WILL NOT INCREASE OR MAINTAIN OUR CUSTOMER BASE OR OUR REVENUES.

    We initially intend to offer our products and services to each other's
customers. We cannot assure you that either of our customers will have any
interest in the other company's products and services. The failure of these
cross-marketing efforts would diminish the benefits realized by this merger.

                                       15
<PAGE>
    In addition, DoubleClick intends after the merger to develop new products
and services that combine the knowledge and resources of the DoubleClick and
Abacus businesses. We cannot offer any assurances that these products or
services will be successful or that we can successfully integrate or realize the
anticipated benefits of the merger. As a result, we may not be able to increase
or maintain our customer base. We cannot assure you that the transactions or
other data in Abacus's database will be predictive or useful in other sales
channels, including Internet advertising. To date, the companies have not
thoroughly investigated the obstacles, technological, market-driven or
otherwise, to developing and marketing these new products and services in a
timely and efficient way. We cannot assure you that DoubleClick will be able to
overcome the obstacles in developing new products and services, or that there
will be a market for the new products or services developed by DoubleClick after
the merger. A failure or inability like this could have a material adverse
effect on the combined company's business, financial condition and operating
results or could result in loss of key personnel. In addition, the attention and
effort devoted to the integration of the two companies will significantly divert
management's attention from other important issues, and could seriously harm the
combined company.

IF THE COSTS ASSOCIATED WITH THE MERGER EXCEED THE BENEFITS REALIZED,
DOUBLECLICK MAY EXPERIENCE INCREASED LOSSES.

    DoubleClick expects to incur a one-time charge of approximately
$16.0 million related to the merger. If the benefits of the merger do not exceed
the costs associated with the merger, including any dilution to DoubleClick's
stockholders resulting from the issuance of shares in connection with the
merger, DoubleClick's financial results could be adversely affected, including
increased losses.

IF DOUBLECLICK DOES NOT SUCCESSFULLY INTEGRATE ABACUS OR THE MERGER'S BENEFITS
DO NOT MEET THE EXPECTATIONS OF FINANCIAL OR INDUSTRY ANALYSTS, THE MARKET PRICE
FOR DOUBLECLICK'S COMMON STOCK MAY DECLINE.

    The market price of DoubleClick common stock may decline as a result of the
merger if:

    - the integration of DoubleClick and Abacus is unsuccessful;

    - DoubleClick does not achieve the perceived benefits of the merger as
      rapidly or to the extent anticipated by financial or industry analysts; or

    - the effect of the merger on DoubleClick's financial results is not
      consistent with the expectations of financial or industry analysts.

IF THE MERGER FAILS TO QUALIFY AS A POOLING OF INTERESTS, DOUBLECLICK WOULD BE
REQUIRED TO TAKE CHARGES AGAINST EARNINGS IN FUTURE PERIODS, WHICH WOULD
INCREASE THE AMOUNT OF ITS LOSSES.

    If we cannot account for the merger as a pooling of interests, a significant
portion of the purchase price for Abacus will be allocated to goodwill and other
intangible assets, which would be amortized by DoubleClick over their estimated
useful lives. As a result, DoubleClick would take charges against its earnings
in the future, which may materially and adversely affect DoubleClick's reported
financial results and, likely, the price of DoubleClick's common stock.

    The availability of pooling-of-interests accounting treatment for the merger
depends upon circumstances and events occurring both before and after the
merger's completion. For example, no significant changes in the business of the
combined company may occur, including significant dispositions of assets, for a
period of two years following the effective time of the merger. Further,
affiliates of DoubleClick and Abacus must not sell any shares of either
DoubleClick or Abacus capital stock for a period beginning before the merger and
ending on the day that DoubleClick publicly announces financial results covering
at least 30 days of combined operations of DoubleClick and Abacus after the
merger. We do not expect that 30 days of combined financial results would be
published sooner than January 2000. If affiliates of

                                       16
<PAGE>
DoubleClick or Abacus sell their shares of DoubleClick common stock prior to
that time, despite a contractual obligation restricting this sale, the merger
may not qualify for accounting as a pooling of interests for financial reporting
purposes.

CHANGING REQUIREMENTS FOR FAIR INFORMATION COLLECTION PRACTICES AND POTENTIALLY
HEIGHTENED SCRUTINY OF OUR PRODUCTS OR SERVICES COULD REQUIRE ADVERSE CHANGES IN
THE WAY THE COMBINED COMPANY CONDUCTS OR PLANS TO CONDUCT ITS BUSINESS.

    There has been public debate about how fair information collection practices
should be formulated for the online and offline collection, distribution and use
of information about a consumer. Some of the discussion has focused on the fair
information collection practices that should apply when information about an
individual that is collected in the offline environment is associated with
information that is collected over the Internet about that individual. Following
the announcement of the Abacus merger with DoubleClick, some of the public
discussion has included, and may continue in the future to include, speculation
about the information collection practices that will be employed in the combined
company's new products and services. DoubleClick has publicly committed that no
personally identifiable offline information about a consumer will be associated
with online information about that consumer for the delivery of personally
targeted Internet advertising without first providing the consumer notice and a
choice to opt out of the targeted advertising. However, as a consequence of
governmental legislation or regulation or evolving standards of fair information
collection practices, the combined company may be required to make changes to
its products or services in ways that could diminish the effectiveness of the
product or service or its attractiveness to potential customers, which could
have a material adverse effect on the combined company.

ABACUS'S OFFICERS AND DIRECTORS HAVE CONFLICTS OF INTEREST THAT MAY INFLUENCE
THEM TO SUPPORT OR APPROVE THE MERGER.

    The directors and officers of Abacus participate in arrangements and have
continuing indemnification against liabilities that provide them with interests
in the merger that are different from, or in addition to, yours. The directors
and officers of Abacus could therefore be more likely to vote to approve the
merger agreement than if they did not hold these interests. Abacus stockholders
should consider whether these interests may have influenced these directors and
officers to support or recommend the merger. See "The Merger--Interests of
Abacus's Officers and Directors in the Merger."

FAILURE TO COMPLETE THE MERGER COULD NEGATIVELY IMPACT ABACUS'S STOCK PRICE AND
OPERATING RESULTS.

    If the merger is not completed for any reason, Abacus may be subject to a
number of material risks, including the following:

    - Abacus may be required to pay DoubleClick a termination fee of
      $30.0 million and reimburse DoubleClick for expenses up to $2.5 million;

    - Abacus may be required to repurchase shares purchased by DoubleClick under
      the stock option agreement;

    - the price of Abacus common stock may decline to the extent that the
      current market price of Abacus common stock reflects a market assumption
      that the merger will be completed; and

    - costs related to the merger, such as legal and accounting fees, must be
      paid even if the merger is not completed.

    If the merger is terminated and Abacus's board of directors determines to
seek another merger or business combination, there can be no assurance that it
will be able to find a partner willing to pay an equivalent or more attractive
price than the price to be paid in the merger. Further, if DoubleClick exercises
its rights under the stock option agreement, Abacus may be precluded in a future
merger or

                                       17
<PAGE>
business combination from accounting for the transaction as a pooling of
interests, which may make Abacus less attractive to potential partners. In
addition, while the merger agreement is in effect, Abacus is prohibited from
soliciting, initiating or encouraging or entering into extraordinary
transactions, such as a merger, sale of assets or other business combination,
with any party other than DoubleClick. As a result of this prohibition, Abacus
will be precluded from discussing potential transactions should the merger not
occur, and may lose an opportunity for a transaction with another potential
partner at a favorable price if the merger is not completed.

UNCERTAINTIES ASSOCIATED WITH THE MERGER MAY CAUSE ABACUS CUSTOMERS AND MEMBERS
OF THE ABACUS ALLIANCE TO DELAY OR DEFER DECISIONS CONCERNING ABACUS OR MAY
CAUSE ABACUS TO LOSE CUSTOMERS.

    Abacus customers and members of the Abacus Alliance may, in response to the
announcement of the merger, delay or defer decisions concerning Abacus. They may
also elect to withdraw from the Abacus Alliance if they perceive a shift in
business away from their market segments. Any delay or deferral in those
decisions by Abacus customers or suppliers could have a material adverse effect
on Abacus's business. For example, Abacus could experience a decrease in
expected revenue as a consequence of the uncertainties associated with the
merger.

UNCERTAINTIES ASSOCIATED WITH THE MERGER MAY CAUSE ABACUS TO LOSE KEY PERSONNEL.

    Current and prospective Abacus employees may experience uncertainty about
their future roles with DoubleClick until DoubleClick's strategies with regard
to Abacus are announced or executed. Any uncertainty may adversely affect
Abacus's ability to attract and retain key management, sales, marketing and
technical personnel.

IF DOUBLECLICK DOES NOT EFFECTIVELY MANAGE THE INTEGRATION OF ACQUIRED COMPANIES
OTHER THAN ABACUS, IT COULD DISRUPT ITS BUSINESS AND CAUSE INCREASED LOSSES.

    As a part of its business strategy, DoubleClick expects to enter into
additional business combinations and acquisitions, including the recently
proposed acquisition of NetGravity. Acquisition transactions require a
significant commitment of resources and are accompanied by a number of risks,
including:

    - the difficulty of assimilating the operations and personnel of the
      acquired companies;

    - the potential disruption of its ongoing business and distraction of
      management;

    - the difficulty of incorporating acquired technology and rights into its
      products and services;

    - unanticipated expenses related to technology integration;

    - the maintenance of uniform standards, controls, procedures and policies;

    - the impairment of relationships with employees and customers as a result
      of any integration of new management personnel; and

    - potential unknown liabilities associated with acquired businesses.

    The combined company may not succeed in addressing these risks or any other
problems encountered in connection with these potential business combinations
and acquisitions, which could disrupt DoubleClick's business and cause increased
losses.

                    RISKS RELATED TO DOUBLECLICK AND ABACUS

    In addition to the risks discussed above, DoubleClick and Abacus are subject
to their own specific risks, including risks relating to their business models,
strategies, markets and legal and regulatory environment. For a detailed
discussion of these risks, please see the risk factors included in each of
DoubleClick's and Abacus's reports filed with the Commission under the
Securities Exchange Act of 1934, which reports are incorporated by reference
into this joint proxy statement/prospectus.

                                       18
<PAGE>
      FORWARD-LOOKING STATEMENTS IN THIS JOINT PROXY STATEMENT/PROSPECTUS

    This joint proxy statement/prospectus and the documents incorporated by
reference into this joint proxy statement/prospectus contain forward-looking
statements within the "safe harbor" provisions of the Private Securities
Litigation Reform Act of 1995 with respect to DoubleClick's and Abacus's
financial condition, results of operations and business and the expected impact
of the merger on DoubleClick's financial performance. Words such as
"anticipates," "expects," "intends," "plans," "believes," "seeks," "estimates"
and similar expressions indicate forward-looking statements. These
forward-looking statements are not guarantees of future performance and are
subject to risks and uncertainties that could cause actual results to differ
materially from the results contemplated by the forward-looking statements. In
evaluating the merger, you should carefully consider the discussion of risks and
uncertainties in the immediately preceding section entitled "Risk Factors."

                                       19
<PAGE>
                              THE SPECIAL MEETINGS

GENERAL

    DOUBLECLICK

    We are furnishing this joint proxy statement/prospectus to holders of
DoubleClick common stock in connection with the solicitation of proxies by the
DoubleClick board of directors for use at the special meeting of stockholders of
DoubleClick to be held on November 23, 1999, and any adjournment or
postponement.

    This joint proxy statement/prospectus is first being furnished to
DoubleClick stockholders on or about October 22, 1999.

    ABACUS

    We are furnishing this joint proxy statement/prospectus to holders of Abacus
common stock in connection with the solicitation of proxies by the Abacus board
of directors for use at the special meeting of stockholders of Abacus to be held
on November 23, 1999, and any adjournment or postponement.

    This joint proxy statement/prospectus is first being furnished to
stockholders of Abacus on or about October 22, 1999. This joint proxy
statement/prospectus is also furnished to Abacus stockholders as a prospectus in
connection with the issuance by DoubleClick of shares of DoubleClick common
stock as contemplated by the merger agreement.

DATE, TIME AND PLACE

    DOUBLECLICK

    The special meeting will be held on November 23, 1999 at 8:30 a.m., local
time, at 80 Fifth Avenue, 17th Floor, New York, New York 10011.

    ABACUS

    The special meeting will be held on November 23, 1999 at 9:00 a.m., local
time, at the Rihga Royal Hotel, 151 West 54th Street, New York, New York 10019.

MATTERS TO BE CONSIDERED AT THE SPECIAL MEETINGS

    DOUBLECLICK

    At the special meeting and any adjournment or postponement, DoubleClick
stockholders will be asked:

    - to consider and vote upon the approval of the issuance of DoubleClick
      common stock as contemplated by the merger agreement;

    - to grant the DoubleClick Board of Directors discretionary authority to
      adjourn the special meeting to solicit additional votes for approval of
      the share issuance;

    - to consider and vote upon a proposal to approve the DoubleClick Inc.
      Employee Stock Purchase Plan; and

    - to transact such other business as may properly come before the special
      meeting.

    ABACUS

    At the Abacus special meeting and any adjournment or postponement of the
special meeting, Abacus stockholders will be asked:

    - to consider and vote upon the adoption of the merger agreement;

    - to grant the Abacus Board of Directors discretionary authority to adjourn
      the special meeting to solicit additional votes for approval of the merger
      agreement; and

                                       20
<PAGE>
    - to transact such other business as may properly come before the special
      meeting.

RECORD DATES

    DOUBLECLICK

    DoubleClick's board has fixed the close of business on October 1, 1999, as
the record date for determining of DoubleClick stockholders entitled to notice
of and to vote at the special meeting.

    ABACUS

    Abacus's board has fixed the close of business on October 1, 1999, as the
record date for determining of Abacus stockholders entitled to notice of and to
vote at the special meeting.

VOTING OF PROXIES

    DOUBLECLICK

    We request that DoubleClick stockholders complete, date and sign the
accompanying proxy and promptly return it in the accompanying envelope or
otherwise mail it to DoubleClick or vote by telephone or over the Internet.
Brokers holding shares in "street name" may vote the shares only if the
beneficial stockholder provides instructions on how to vote. Brokers will
provide beneficial owners instructions on how to direct the brokers to vote the
shares. All properly executed proxies that DoubleClick receives prior to the
vote at the special meeting, and that are not revoked, will be voted in
accordance with the instructions indicated on the proxies. If no direction is
indicated, the proxies will be voted (A) to approve the issuance of shares of
DoubleClick as contemplated by the merger agreement, (B) to approve the proposal
to grant the board discretionary authority to adjourn the special meeting and
(C) to approve the DoubleClick Inc. Employee Stock Purchase Plan. DoubleClick's
board does not currently intend to bring any other business before the special
meeting. As far as DoubleClick's board knows, no other matters are to be brought
before the special meeting. If other business properly comes before the special
meeting or any postponement or adjournment, the proxies will vote in accordance
with their own judgment.

    Stockholders may revoke their proxies at any time prior to its use

    - by delivering to the Secretary of DoubleClick a signed notice of
      revocation or a later-dated, signed proxy; or

    - by attending the special meeting and voting in person.

Attendance at the special meeting does not in itself constitute the revocation
of a proxy.

    ABACUS

    We request that Abacus stockholders complete, date and sign the accompanying
proxy and promptly return it in the accompanying envelope or otherwise mail it
to Abacus. Brokers holding shares in "street name" may vote the shares only if
the beneficial stockholder provides instructions on how to vote. Brokers will
provide beneficial owners instructions on how to direct the brokers to vote the
shares. All properly executed proxies that Abacus receives prior to the vote at
the special meeting, and that are not revoked, will be voted in accordance with
the instructions indicated on the proxies or, if no direction is indicated, to
approve the merger agreement and the merger. Abacus's board does not currently
intend to bring any other business before the special meeting and, so far as
Abacus's board knows, no other matters are to be brought before the special
meeting. If other business properly comes before the special meeting or any
postponement or adjournment, the proxies will vote in accordance with their own
judgment.

    Stockholders may revoke their proxies at any time prior to its use

    - by delivering to the Secretary of Abacus a signed notice of revocation or
      a later-dated, signed proxy; or

    - by attending the special meeting and voting in person.

Attendance at the special meeting does not in itself constitute the revocation
of a proxy.

                                       21
<PAGE>
VOTES REQUIRED

    DOUBLECLICK

    As of the close of business on October 1, 1999, there were 39,914,830 shares
of DoubleClick common stock outstanding and entitled to vote. The holders of a
majority of the shares of DoubleClick common stock entitled to vote and that are
present or represented by proxy at the DoubleClick meeting must (A) approve the
issuance of DoubleClick common stock in the merger, (B) approve the proposal to
grant the board discretionary authority to adjourn the special meeting and (C)
approve the Employee Stock Purchase Plan. DoubleClick stockholders have one vote
per share of DoubleClick common stock owned on the record date.

    As of October 1, 1999, directors and executive officers of DoubleClick and
their affiliates beneficially owned an aggregate of 6,450,546 shares of
DoubleClick common stock (exclusive of any shares issuable upon the exercise of
options) or approximately 16.2% of the shares of DoubleClick common stock
outstanding on that date. The directors and executive officers of DoubleClick
have indicated their intention to vote their shares of DoubleClick common stock
in favor of the issuance of the shares of DoubleClick common stock as
contemplated by the merger agreement. As of October 1, 1999, directors and
executive officers of Abacus owned no shares of DoubleClick common stock.

    ABACUS

    As of the close of business on October 1, 1999, there were 9,949,209 shares
of Abacus common stock outstanding and entitled to vote. The holders of a
majority of the outstanding shares of Abacus common stock must approve the
merger agreement and the merger. The vote required to grant to the Abacus board
of directors discretionary authority to adjourn the special meeting for the
solicitation of additional votes is a majority of shares actually voted at the
special meeting where a quorum is present. Abacus stockholders have one vote per
share of Abacus common stock owned on the record date.

    As of October 1, 1999, directors and executive officers of Abacus and their
affiliates beneficially owned an aggregate of 505,500 shares of Abacus common
stock (exclusive of any shares issuable upon the exercise of options) or
approximately 5.1% of the shares of Abacus common stock outstanding on that
date. The directors and executive officers of Abacus have indicated their
intention to vote their shares of Abacus common stock in favor of the merger
agreement. Under a stockholder agreement in the form attached as APPENDIX C to
this joint proxy statement/prospectus, Abacus stockholders owning approximately
5% of Abacus's common stock outstanding as of June 13, 1999, excluding any
shares issuable upon the exercise of options, have agreed to vote all of their
shares of Abacus common stock for approval of the merger agreement and the
merger. As of October 1, 1999, directors and executive officers of DoubleClick
owned no shares of Abacus common stock. See "The Merger--Interests of Abacus's
Officers and Directors in the Merger."

QUORUM; ABSTENTIONS AND BROKER NON-VOTES

    DOUBLECLICK

    The required quorum for the transaction of business at the special meeting
is a majority of the shares of DoubleClick common stock issued and outstanding
on the record date. Abstentions and broker non-votes each will be included in
determining the number of shares present and voting at the meeting for the
purpose of determining the presence of a quorum. Brokers holding shares for
beneficial owners cannot vote on the actions proposed in this joint proxy
statement/prospectus without the owners' specific instructions. Accordingly,
DoubleClick stockholders are urged to return the enclosed proxy card marked to
indicate their vote. Broker non-votes will not be included in vote totals and
will have no effect on the outcome of the votes on the issuance of the shares in
the merger or the proposal to grant the board discretionary authority to adjourn
the special meeting. Abstentions, however, will have the same effect as a vote
against these proposals.

                                       22
<PAGE>
    ABACUS

    The required quorum for the transaction of business at the special meeting
is one-third of the shares of Abacus common stock issued and outstanding on the
record date. Abstentions and broker non-votes each will be included in
determining the number of shares present and voting at the meeting for the
purpose of determining the presence of a quorum. Because approval of the merger
agreement and the consummation of the merger requires the affirmative vote of a
majority of the outstanding shares of Abacus common stock entitled to vote,
abstentions and broker non-votes will have the same effect as votes against the
merger agreement and the consummation of the merger. In addition, the failure of
an Abacus stockholder to return a proxy or vote in person will have the effect
of a vote against the approval of the merger agreement and the merger. Broker
non-votes will not be included in the vote totals and will have no effect on the
outcome of the votes on the proposal to grant the board discretionary authority
to adjourn the special meeting. Abstentions, however, will have the same effect
as a vote against this proposal. Brokers holding shares for beneficial owners
cannot vote on the actions proposed in this joint proxy statement/prospectus
without the owners' specific instructions. Accordingly, Abacus stockholders are
urged to return the enclosed proxy card marked to indicate their vote.

SOLICITATION OF PROXIES AND EXPENSES

    DoubleClick and Abacus have independently retained D.F. King to assist in
the solicitation of proxies from their stockholders. The fees to be paid to for
D.F. King's services are not expected to exceed $  in the aggregate, plus
reasonable out-of-pocket expenses. DoubleClick and Abacus will each bear their
own expenses in connection with the solicitation of proxies for their special
meetings of stockholders, except that each will pay one-half of all printing and
filing costs and expenses incurred in connection with the registration statement
and this joint proxy statement/prospectus.

    In addition to solicitation by mail, the directors, officers and employees
of DoubleClick and Abacus may each solicit proxies from their stockholders by
telephone, facsimile, e-mail or in person. Brokerage houses, nominees,
fiduciaries and other custodians will be requested to forward soliciting
materials to beneficial owners and will be reimbursed for their reasonable
expenses incurred in sending proxy materials to beneficial owners.

BOARD RECOMMENDATIONS

    DOUBLECLICK

    THE DOUBLECLICK BOARD HAS DETERMINED THAT THE MERGER AGREEMENT AND THE
MERGER ARE FAIR TO, AND IN THE BEST INTERESTS OF, DOUBLECLICK AND ITS
STOCKHOLDERS. ACCORDINGLY, THE BOARD HAS UNANIMOUSLY APPROVED THE MERGER
AGREEMENT AND UNANIMOUSLY RECOMMENDS THAT STOCKHOLDERS VOTE FOR APPROVAL OF THE
ISSUANCE OF SHARES OF DOUBLECLICK COMMON STOCK AS CONTEMPLATED BY THE MERGER
AGREEMENT.

    THE DOUBLECLICK BOARD HAS DETERMINED THAT IMPLEMENTING A PROGRAM OF STOCK
OWNERSHIP FOR DOUBLECLICK'S EMPLOYEES IS IN DOUBLECLICK'S BEST INTERESTS.
ACCORDINGLY, THE DOUBLECLICK BOARD UNANIMOUSLY RECOMMENDS THAT STOCKHOLDERS VOTE
FOR APPROVAL OF THE DOUBLECLICK INC. EMPLOYEE STOCK PURCHASE PLAN.

    THE MATTERS TO BE CONSIDERED AT THE SPECIAL MEETING ARE OF GREAT IMPORTANCE
TO DOUBLECLICK STOCKHOLDERS. ACCORDINGLY, DOUBLECLICK STOCKHOLDERS ARE URGED TO
READ AND CAREFULLY CONSIDER THE INFORMATION PRESENTED IN THIS JOINT PROXY
STATEMENT/PROSPECTUS, AND TO COMPLETE, DATE, SIGN AND PROMPTLY RETURN THE
ENCLOSED PROXY IN THE ENCLOSED POSTAGE-PAID ENVELOPE.

    DOUBLECLICK STOCKHOLDERS SHOULD NOT SEND ANY STOCK CERTIFICATES WITH THEIR
PROXY CARDS.

    ABACUS

    THE ABACUS BOARD HAS DETERMINED THAT THE MERGER AGREEMENT AND THE MERGER ARE
FAIR TO, AND IN THE BEST INTERESTS OF, ABACUS AND ITS STOCKHOLDERS. ACCORDINGLY,
THE BOARD HAS UNANIMOUSLY APPROVED THE MERGER

                                       23
<PAGE>
AGREEMENT AND UNANIMOUSLY RECOMMENDS THAT STOCKHOLDERS VOTE FOR APPROVAL OF THE
MERGER AGREEMENT AND THE MERGER. In considering this recommendation, Abacus
stockholders should be aware that Abacus's directors and officers have interests
in the merger that are different from, or in addition to, those of Abacus's
stockholders, and that DoubleClick has agreed to provide employment, severance
and indemnification arrangements to the directors and officers of Abacus. See
"The Merger--Interests of Abacus's Officers and Directors in the Merger."

    THE MATTERS TO BE CONSIDERED AT THE SPECIAL MEETING ARE OF GREAT IMPORTANCE
TO THE STOCKHOLDERS OF ABACUS. ACCORDINGLY, ABACUS STOCKHOLDERS ARE URGED TO
READ AND CAREFULLY CONSIDER THE INFORMATION PRESENTED IN THIS JOINT PROXY
STATEMENT/PROSPECTUS, AND TO COMPLETE, DATE, SIGN AND PROMPTLY RETURN THE
ENCLOSED PROXY IN THE ENCLOSED POSTAGE-PAID ENVELOPE.

    ABACUS' STOCKHOLDERS SHOULD NOT SEND ANY STOCK CERTIFICATES WITH THEIR PROXY
CARDS. A transmittal form with instructions for the surrender of Abacus common
stock certificates will be mailed to Abacus stockholders promptly after
completion of the merger. For more information regarding the procedures for
exchanging Abacus stock certificates for DoubleClick stock certificates, see
"The Merger Agreement and Related Agreements--Exchange of Abacus Stock
Certificates for DoubleClick Stock Certificates."

                                       24
<PAGE>
                                   THE MERGER

    THIS SECTION OF THE JOINT PROXY STATEMENT/PROSPECTUS DESCRIBES MATERIAL
ASPECTS OF THE PROPOSED MERGER, INCLUDING THE MERGER AGREEMENT AND THE STOCK
OPTION AGREEMENT. WHILE WE BELIEVE THAT THE DESCRIPTION COVERS THE MATERIAL
TERMS OF THE MERGER AND THE RELATED TRANSACTIONS, THIS SUMMARY MAY NOT CONTAIN
ALL OF THE INFORMATION THAT IS IMPORTANT TO DOUBLECLICK STOCKHOLDERS AND ABACUS
STOCKHOLDERS. STOCKHOLDERS SHOULD READ THE MERGER AGREEMENT, STOCK OPTION
AGREEMENT AND THE OTHER DOCUMENTS WE REFER TO CAREFULLY AND IN THEIR ENTIRETY
FOR A MORE COMPLETE UNDERSTANDING OF THE MERGER.

BACKGROUND OF THE MERGER

    On January 25, 1999, Kevin O'Connor, DoubleClick's Chief Executive Officer,
called M. Anthony White, Chairman of the Board and Chief Executive Officer of
Abacus to set up a meeting for January 27 to discuss potential ways in which
DoubleClick and Abacus could work together in 1999. At this January 27 meeting,
Mr. O'Connor proposed, and Mr. White agreed to, a follow-up meeting to be held
on January 30, 1999 with several senior executives of each company.

    On January 30, 1999, Mr. O'Connor, along with Jeff Epstein, DoubleClick's
Executive Vice President, Jonathan Shapiro, DoubleClick's Vice President,
Business Development, David Rosenblatt, DoubleClick's Vice President and General
Manager, Closed Loop Marketing, and Jennifer Haggerty, DoubleClick's Director of
Strategic Development, met at DoubleClick's New York offices with Mr. White, Dan
Snyder, Abacus's President--New Markets and Chairman--Abacus Europe, and Carlos
Sala, Abacus's Senior Vice President--Finance, Chief Financial Officer,
Secretary and Treasurer. At this meeting, the parties provided overviews of
their companies and discussed the potential for developing Internet-based
products based on Abacus's core business, and cross-marketing opportunities for
the companies' existing products and for products to be jointly developed.

    On February 4, 1999, Mr. O'Connor, Kevin Ryan, DoubleClick's President and
Chief Operating Officer, Mr. Epstein and Ms. Haggerty, together with a
representative of Goldman Sachs, DoubleClick's financial advisor, met with
Messrs. White, Snyder and Sala at Abacus's offices in Westminster, Colorado to
continue the discussions from January 30, 1999.

    On February 5, 1999 at a regularly scheduled DoubleClick board meeting,
members of senior management, together with representatives of Goldman Sachs,
presented to the board a list of several companies, including Abacus, to
approach for joint business opportunities and potential strategic partnerships.
The board did not take any formal action on this matter at this meeting.

    On February 8, 1999 in person and on February 10, 1999 by telephone,
Mr. O'Connor and Mr. White continued to discuss the same alternative business
ventures discussed in the January 30, 1999 meeting.

    On February 15, 1999, Abacus's board of directors held a special meeting
which was attended by the company's legal advisors and BancBoston Robertson
Stephens to discuss the relative merits of potential strategic alternatives.
These alternatives included business combinations, joint ventures and strategic
alliances to enable the application of Abacus products and services to
electronic commerce over the Internet and to enable Abacus to develop an online
targeting, profiling and e-mail delivery capability to facilitate the
development of products and services to existing and new customers in direct
marketing electronic commerce. BancBoston Robertson Stephens presented analyses
of these alternatives. The board authorized Mr. White to continue exploratory
strategic discussions with a range of parties. On February 16, 1999, the Abacus
board engaged BancBoston Robertson Stephens as Abacus's exclusive financial
advisor to assist Abacus's senior management and board in evaluating strategic
alternatives for Abacus.

    Between February 1999 and June 1999, Abacus continued to hold discussions
with six companies regarding various strategic alternatives, including business
combinations as well as joint ventures, strategic

                                       25
<PAGE>
investments and alliances involving the application of Abacus products and
services to electronic commerce over the Internet. One of the alternatives being
considered was a possible joint venture between Abacus and DoubleClick to
provide online targeted advertising.

    On February 16, 1999, Messrs. O'Connor and Ryan, Dwight Merriman,
DoubleClick's Chief Technical Officer, Mr. Epstein, Mr. Rosenblatt and
Ms. Haggerty, together with a representative of Goldman Sachs, DoubleClick's
financial advisor, met with Messrs. White, Snyder and Sala and a representative
of BancBoston Robertson Stephens, Abacus's financial advisor, in New York at the
offices of Kane Kessler, Abacus's legal counsel, to discuss a potential joint
venture, cooperative product development or other strategic initiative.
Mr. White indicated to Mr. O'Connor that he would be open to a business
combination. The parties had a preliminary discussion regarding a potential
business combination, but did not discuss any principal terms. On February 17,
1999, Mr. O'Connor met with Mr. White to continue the prior day's discussions.
At this meeting, Mr. O'Connor indicated that DoubleClick was not interested at
this time in contemplating a business combination with Abacus, but would like to
pursue the possibility of a joint venture. DoubleClick was not interested in
pursuing a business combination with Abacus because there was a lack of
consensus among DoubleClick's executive team to proceed with this type of
transaction, and at that time, DoubleClick had not sufficiently developed its
rationale and strategy for a business combination with Abacus.

    On February 17 and 24, 1999, Abacus's senior management and BancBoston
Robertson Stephens met with an Internet company other than DoubleClick to
explore the possibility of a joint venture between the two companies.

    On March 2, 1999, Mr. O'Connor and Mr. White had a telephone conversation
about the potential of forming a joint venture partnership. They agreed to meet
on March 18, 1999.

    From March 3, 1999 through March 13, 1999, Abacus's senior management and
its legal and financial advisors pursued strategic alternatives with a leading
Internet portal that was a public company. Abacus and the Internet portal
discussed a transaction in which the Internet portal company would acquire
Abacus in a merger in which the Internet portal company would issue its common
stock to Abacus stockholders in exchange for their Abacus stock. The parties
ended their discussions on March 13, 1999 primarily because they could not agree
on an appropriate exchange ratio, and could not agree on marketing strategies
for the combined company, and because of Abacus management's uncertainties with
respect to the corporate structure of the Internet portal company. In this
period, Abacus had no contact with DoubleClick.

    On March 18, 1999, Mr. O'Connor and Mr. White continued discussions relating
to the formation of a DoubleClick-Abacus joint venture.

    On April 14, 1999, Messrs. O'Connor, Merriman, Ryan, Epstein and Shapiro and
Ms. Haggerty met with Messrs. White, Snyder and Sala and Janie Smith, Abacus's
Vice President, Internet, at Abacus's offices in New York to discuss the
formation of a joint venture between the two companies.

    On April 21 and 22, 1999, Messrs. Epstein and Shapiro met with Ms. Smith in
Colorado to further discuss the possibility of a joint venture.

    On April 29, 1999, Messrs. O'Connor, Shapiro, White and Sala and Ms. Smith
met at DoubleClick's offices to continue discussions to develop more detailed
plans for a joint venture between the companies.

    From May 10 through May 13, 1999, Mr. Shapiro and Ms. Smith prepared a
business plan for a joint venture between DoubleClick and Abacus. This plan was
presented to Messrs. O'Connor, Epstein, White and Sala and Ms. Haggerty on
May 14, 1999.

    On May 27, 1999, a large group of DoubleClick executives traveled to
Abacus's offices in Broomfield, Colorado to meet with Abacus's senior management
to discuss the products that could be jointly developed in a collaboration
between DoubleClick and Abacus, and also reviewed opportunities for cross
marketing.

                                       26
<PAGE>
    On June 5, 1999, Mr. O'Connor and other DoubleClick executives updated
DoubleClick board members as to the status of their discussions with Abacus
regarding various business opportunities, including a potential joint venture,
and DoubleClick management indicated to the DoubleClick board that they would be
interested in pursuing a business combination with Abacus. When DoubleClick and
Abacus were structuring the joint venture, it became clear that both parties
wanted to lead the venture. DoubleClick's executives believed that the corporate
ownership and corporate governance issues in a joint venture could not be
resolved in a manner that would provide appropriate incentives to both parties
to work toward the success of the joint efforts. DoubleClick's executives
concluded that DoubleClick could avoid these difficult issues by acquiring
Abacus. DoubleClick's board did not take any formal action at this time.

    On June 7, 1999, Messrs. O'Connor, Ryan and Epstein, Ms. Haggerty and
representatives from Goldman Sachs met with Messrs. White and Sala and
representatives of BancBoston Robertson Stephens in New York at the offices of
Brobeck, Phleger & Harrison LLP, DoubleClick's legal counsel, to continue
discussing the potential joint venture. At this meeting, DoubleClick informed
Abacus that it would be interested in contemplating a business combination and
presented the terms upon which DoubleClick would be willing to consider this
transaction. The terms included DoubleClick's acquiring Abacus in a
stock-for-stock merger to be treated as a pooling-of-interests for accounting
purposes. The parties discussed the business combination proposal throughout the
day. On June 8, 1999, the parties continued these discussions and by early
evening, had determined that the stage of their discussions justified commencing
mutual due diligence and negotiating definitive documentation, all subject to
the approval of each company's board of directors. The parties also agreed that
Abacus would enter into a limited duration exclusivity agreement with
DoubleClick.

    On June 9, 1999, Brobeck, Phleger & Harrison delivered to Abacus a draft
merger agreement and related documents, including a stock option agreement
giving DoubleClick the right to purchase Abacus shares in circumstances
involving a competing fundamental transaction with Abacus, and voting agreements
with Abacus's management. DoubleClick and Abacus began business, legal and
financial due diligence of each other, which continued through the morning of
June 13, 1999. Also during this period, senior management of both companies held
numerous discussions regarding various business, financial, operational and
technical issues involved in combining the companies.

    On June 10, 1999, a special committee of Abacus's board of directors
consisting of Messrs. Kenny and Lee held a special meeting to discuss the status
of the responses from various parties interested in creating a strategic
alliance or entering into a business combination with Abacus. The special
committee was formed on February 15, 1999, but did not meet formally until
June 10, 1999 because all deliberations prior to June 10, 1999, concerning the
subject matter with respect to which the special committee was empowered to act
were considered by the full board. At the meeting of June 10, 1999, the special
committee, together with Abacus's legal and financial advisors, held an
extensive discussion evaluating the relative merits of the potential
alternatives, including the valuation and volatility risks relating to the
potential acquirors' stock, the likely timing of, and risks to, closing each
transaction, and the likelihood of success of the transaction after
consummation. Only one transaction, involving a proposed joint venture regarding
application of Abacus's database and products and services to direct marketing
over the Internet, was advanced enough to consider relative to the status and
nature of discussions with DoubleClick. The proposed joint venture partner was a
leading, publicly held technology company. The special committee was not
satisfied that the proposed joint venture could be successfully established or
operated because of differences relating to financial guarantees, the level of
commitment in technology and human resources, and revenue sharing and
termination provisions of the joint venture. Following the discussion, the
special committee unanimously agreed that the DoubleClick proposal constituted a
superior transaction because of the synergies between the two companies,
including the complementary nature of the companies' products, the price and
other terms offered, and the commitment of the parties to close the transaction
and develop new products likely to be successful. The synergies and
complementary

                                       27
<PAGE>
nature of products and services between Abacus and DoubleClick were superior to
the other possible transaction partners for the following reasons:

    - Abacus and DoubleClick are both independent companies, not affiliated with
      other parties, unlike the two Internet portal companies that were being
      considered;

    - the Abacus client base has little or no conflict with the DoubleClick
      client base, whereas the Internet portal company and technology company
      had relationships with online merchants that compete with Abacus clients;

    - DoubleClick's clients are interested in targeted services that Abacus can
      provide;

    - DoubleClick has a data strategy and data technology that is compatible
      with Abacus's business;

    - DoubleClick has advertising management and delivery capabilities that
      Abacus's clients need; and

    - Abacus has data collection capabilities that DoubleClick is seeking.

The special committee then authorized Mr. White and a team of Abacus's legal and
financial advisors to enter into a non-solicitation agreement with DoubleClick,
to expire on June 16, 1999, during which period Abacus would not be permitted to
negotiate with, or provide information to, any other party regarding a business
combination transaction.

    From June 11, 1999 through June 13, 1999, representatives of DoubleClick and
Abacus, together with their financial and legal advisors, held numerous meetings
to discuss and negotiate the terms and conditions of the merger agreement, the
stock option agreement and various other legal and financial issues, the terms
of which were finalized on June 13, 1999 in the afternoon.

    On June 12, 1999, the board of directors of Abacus held a special meeting.
Abacus's legal counsel reviewed the principal terms of the merger agreement and
the related agreements. Abacus's management, legal advisors and financial
advisors reported on the results of their due diligence reviews of DoubleClick.
BancBoston Robertson Stephens then made a presentation to the board regarding
the financial analyses it had performed in connection with its opinion and
stated orally that it was prepared to render, and subsequently did provide, its
written opinion, to the effect that as of June 13, 1999, and based on the
assumptions made, matters considered, and limits of its review as set forth in
its opinion, the share exchange ratio in the merger was fair to Abacus's
stockholders from a financial point of view. Following a discussion, the Abacus
board stated that it was prepared to approve the final terms of the merger
agreement and related agreements, subject to the resolution of several
transaction issues, including those relating to representations and warranties,
and terms and conditions under which termination fees would be payable by Abacus
in the event of the termination of the merger agreement which the parties were
then negotiating. This meeting was adjourned until June 13, 1999.

    On June 13, 1999 the board of directors of Abacus reconvened the special
meeting begun on June 12. Abacus management, legal advisors and financial
advisors updated the board on negotiations and related transaction issues.
Following a discussion, the Abacus board unanimously approved the final terms of
the merger agreement and related agreements and determined to recommend that the
Abacus stockholders approve the merger.

    The DoubleClick board held a special meeting on June 13, 1999. DoubleClick's
management and legal advisors then reported on the results of their due
diligence investigations of Abacus. Brobeck, Phleger & Harrison outlined the
directors' legal duties and responsibilities in connection with considering the
merger and reviewed the principal terms of the merger agreement and related
agreements. A representative of PricewaterhouseCoopers LLP then discussed the
accounting treatment of the proposed merger. Goldman Sachs then summarized the
material financial analyses that it performed with respect to the proposed
merger. Goldman Sachs then delivered its oral opinion to the DoubleClick board
that, as of June 13, 1999, the share exchange ratio was fair from a financial
point of view to DoubleClick. Goldman

                                       28
<PAGE>
Sachs subsequently confirmed its oral opinion by delivery of its written
opinion, dated June 13, 1999, which sets forth assumptions made, matters
considered and limitations on the review undertaken in connection with the
opinion.

    Following these presentations, DoubleClick's board engaged in a full
discussion of the terms of the proposed merger, including the strategic benefits
of the combination, the terms and conditions of the proposed merger agreement
and the analyses and opinion of Goldman Sachs. Following the discussion, the
DoubleClick board unanimously approved the merger agreement and related
agreements, and the issuance of DoubleClick common stock in the merger. The
DoubleClick board determined to recommend that the DoubleClick stockholders
approve the issuance of shares of DoubleClick common stock in the merger.

    The merger agreement, the stock option agreement and related transaction
documents were signed by the parties late in the afternoon of June 13, 1999.
DoubleClick and Abacus issued a joint press release announcing the merger on the
morning of June 14, 1999.

    Subsequent to June 14, 1999, during the course of its consideration of the
NetGravity transaction, the DoubleClick board discussed the fit of NetGravity in
the combined DoubleClick-Abacus company, and concluded that the NetGravity
transaction would not have a negative impact on the merger with Abacus.

    The Abacus board and senior management of Abacus considered the impact of
the NetGravity merger on the DoubleClick/Abacus merger. Considering the
relatively smaller size of the NetGravity merger (NetGravity stockholders will
acquire approximately 9% of the outstanding DoubleClick shares, assuming
completion of the DoubleClick/Abacus merger and the NetGravity merger), and the
business in which NetGravity is engaged, Abacus was satisfied that the
NetGravity merger would not be materially adverse to the Abacus/DoubleClick
combined company or the fairness of the merger to Abacus stockholders.

REASONS FOR THE MERGER; RECOMMENDATIONS OF BOARDS OF DIRECTORS

    DOUBLECLICK

    The DoubleClick board unanimously concluded that the merger was advisable
and fair to, and in the best interests, of DoubleClick and its stockholders and
determined to recommend that the stockholders approve the issuance of the shares
of DoubleClick common stock in the merger.

    The decision by DoubleClick's board was based on several potential benefits
of the merger that it believes will contribute to the success of the combined
company. These potential benefits include:

    - creating a market leader in all three segments of Internet advertising
      infrastructure: data, technology and media;

    - providing highly efficient, targeted and measurable marketing and
      advertising solutions through the Internet and other media;

    - accelerating DoubleClick's growth rate;

    - potentially shortening the period of operating at a loss; and

    - positioning DoubleClick to benefit from the expanding e-commerce market
      and the emergence of broadband Internet services.

    DoubleClick's board reviewed a number of factors in evaluating the merger,
including, but not limited to, the following:

    - historical information concerning DoubleClick's and Abacus's businesses,
      financial performance and condition, operations, technology and
      management;

                                       29
<PAGE>
    - DoubleClick's management's view of the financial condition, results of
      operations and businesses of DoubleClick and Abacus before and after
      giving effect to the merger and the DoubleClick board's determination of
      the merger's effect on stockholder value;

    - current financial market conditions and historical stock market prices,
      volatility and trading information;

    - the determination of Abacus's senior management to enter new employment
      agreements and non-competition and non-disclosure agreements to be
      effective upon consummation of the merger;

    - the consideration Abacus stockholders will receive in the merger in light
      of comparable merger transactions analyzed by Goldman Sachs in connection
      with providing its fairness opinion to the DoubleClick board;

    - the opinion of Goldman Sachs that, as of the date of its opinion and
      subject to the assumptions made, matters considered and limitations of the
      review undertaken in connection with the opinion, as set forth in the
      opinion, the share exchange ratio in the merger was fair from a financial
      point of view to DoubleClick;

    - the belief that the terms of the merger agreement and the stock option
      agreement are reasonable;

    - the impact of the merger on DoubleClick's customers and employees;

    - results of the due diligence investigation conducted by DoubleClick's
      management, accountants and counsel as to the results of the due diligence
      investigation of Abacus; and

    - the expectation that the merger will be accounted for as a pooling of
      interests.

    The DoubleClick board also identified and considered a number of potentially
negative factors in its deliberations concerning the merger including the
following:

    - the risk that the potential benefits of the merger may not be realized;

    - the possibility that the merger may not be consummated, even if approved
      by DoubleClick's and Abacus's stockholders;

    - the potential heightened attention on consumers' privacy concerns;

    - the risk of management and employee disruption associated with the merger,
      including the risk that despite the efforts of the combined company, key
      technical, sales and management personnel might not remain employed by the
      combined company; and

    - other applicable risks described in this joint proxy statement/prospectus
      under "Risk Factors."

    DoubleClick's board concluded, however, that, on balance, the merger's
potential benefits to DoubleClick and its stockholders outweighed the associated
risks. This discussion of the information and factors considered by
DoubleClick's board is not intended to be exhaustive. In view of the variety of
factors considered in connection with its evaluation of the merger,
DoubleClick's board did not find it practicable to, and did not quantify or
otherwise assign relative weight to, the specific factors considered in reaching
its determination.

    FOR THE REASONS DISCUSSED ABOVE, DOUBLECLICK'S BOARD OF DIRECTORS HAS
DETERMINED THE MERGER AGREEMENT AND THE MERGER TO BE ADVISABLE AND FAIR TO, AND
IN THE BEST INTERESTS OF, DOUBLECLICK'S STOCKHOLDERS. IN CONNECTION WITH THE
MERGER, DOUBLECLICK'S BOARD OF DIRECTORS RECOMMENDS APPROVAL OF THE ISSUANCE OF
SHARES OF DOUBLECLICK COMMON STOCK AS CONTEMPLATED BY THE MERGER AGREEMENT.

                                       30
<PAGE>
    ABACUS

    The Abacus board determined to enter into the merger agreement and to
recommend that Abacus stockholders approve the merger agreement in pursuit of
its strategy to exploit opportunities over the Internet. Abacus determined the
need to pursue an Internet strategy in order to:

    - benefit from the potential revenue created by integrating Abacus's
      transactional data into online services; and

    - expand the business model into a new market and provide existing customers
      access to transactional data derived from Internet e-commerce and a new
      distribution medium for products and customers.

    The decision of the Abacus board was the result of its careful consideration
of a range of strategic alternatives, including potential business combinations
and relationships with DoubleClick and other companies in the pursuit of a
long-term Internet business strategy for Abacus.

    The Abacus board's primary consideration was to identify and secure the
alternative that would provide the best strategic fit for Abacus and to provide
long-term stockholder value to Abacus stockholders. In this regard, the Abacus
board concluded that the DoubleClick merger represents the best transaction
among several alternatives considered by the Abacus board. In reaching this
determination, the Abacus board considered the following factors:

    - the price per share implied by the exchange ratio in the merger, as of the
      last trading day prior to the announcement of the merger, which the board
      determined represents: (A) a premium of more than 25% over the closing
      price of Abacus common stock, and (B) a premium of more than 44% over the
      average closing price in the prior 30 trading days;

    - the exchange ratio in the merger and implied per share price, which
      compares favorably according to a number of applicable valuation
      methodologies, including the analysis of companies comparable to Abacus
      and transactions comparable to the merger used by BancBoston Robertson
      Stephens in connection with providing its fairness opinion to the Abacus
      board; and

    - the opinion of BancBoston Robertson Stephens, delivered in writing on
      June 13, 1999, that as of June 13, 1999, and subject to assumptions made,
      matters considered and limitations on the review set forth in its opinion,
      the share exchange ratio in the merger is fair to Abacus stockholders from
      a financial point of view. Please see "Opinions of Financial
      Advisors--Abacus."

    The Abacus board also believes that the merger will provide the opportunity
to:

    - combine DoubleClick's online behavioral and Internet data with Abacus's
      transactional purchasing data to create an improved model for targeted
      advertising;

    - realize potentially significant synergies and operating benefits;

    - improve rates for targeted Web advertising;

    - offer new products to Abacus's customers; and

    - increase Abacus's revenue growth rate.

    In reviewing its alternatives and making its determination, the Abacus board
reviewed:

    - the results of the due diligence review by Abacus's management, legal
      advisors and financial advisors regarding DoubleClick's business,
      operations, technology and competitive position;

    - possible synergistic and expansion opportunities for the combined company;

    - the current and prospective business environment in which Abacus operates;
      and

                                       31
<PAGE>
    - the competitive environment for online advertising targeting companies and
      portals generally and the trend of these companies toward developing a
      data strategy.

    The Abacus board also reviewed with its legal advisors:

    - the terms and conditions of the merger agreement;

    - voting agreements;

    - the stock option covering shares of Abacus granted to DoubleClick in
      connection with the merger agreement;

    - the events triggering payment of the termination fee; and

    - the limitations on the ability of Abacus to negotiate with other companies
      regarding an alternative transaction, and the potential effect these
      provisions would have on Abacus's receiving alternative proposals that
      could be superior to the merger with DoubleClick.

    The Abacus board also considered a number of potentially negative factors in
its deliberations concerning the merger, including:

    - the risk that because the exchange ratio will not be adjusted for changes
      in the market price of either DoubleClick common stock or Abacus common
      stock, the per share value of the consideration to be received by Abacus
      stockholders might be significantly less than the price per share implied
      by the exchange ratio immediately prior to the announcement of the merger;

    - the relative volatility of the market value of DoubleClick common stock
      compared to the securities of other companies with whom Abacus was
      considering a business combination transaction and other companies that
      are similar to DoubleClick, which companies were the same as those used by
      BancBoston Robertson Stephens for the analysis underlying its opinion;

    - the risk that the merger might not be consummated;

    - the potential loss of revenues and business opportunities for Abacus as a
      result of confusion in the marketplace as a result of the announcement of
      the merger, and the possible exploitation of this confusion by Abacus's
      and DoubleClick's competitors;

    - the possibility of management disruption associated with the merger and
      integrating the operations of the companies, and the risk that, despite
      the efforts of the combined company, key management and technical
      personnel of Abacus might not continue with the combined company;

    - the risk that the benefits sought to be achieved by the merger will not be
      realized; and

    - other applicable risks described in this joint proxy statement/prospectus
      under "Risk Factors."

    After carefully evaluating these factors, both positive and negative, the
board of directors of Abacus has determined that the merger is in the best
interests of Abacus and its stockholders and unanimously recommends that Abacus
stockholders vote for approval and adoption of the merger agreement and approval
of the merger.

    FOR THE REASONS DISCUSSED ABOVE, ABACUS'S BOARD OF DIRECTORS HAS UNANIMOUSLY
APPROVED THE MERGER AGREEMENT AND HAS DETERMINED THAT THE MERGER IS ADVISABLE
AND FAIR TO, AND IN THE BEST INTERESTS OF, ABACUS AND ITS STOCKHOLDERS AND
UNANIMOUSLY RECOMMENDS THAT ABACUS STOCKHOLDERS VOTE FOR APPROVAL OF THE MERGER
AGREEMENT AND THE MERGER.

    In considering the recommendation of Abacus's board with respect to the
merger agreement, Abacus stockholders should be aware that Abacus's directors
and officers have interests in the merger that are different from, or are in
addition to, the interests of Abacus stockholders generally. Please see "The
Merger--Interests of Abacus's Officers and Directors in the Merger."

                                       32
<PAGE>
OPINIONS OF FINANCIAL ADVISORS

    DOUBLECLICK

    On June 13, 1999, Goldman Sachs delivered its oral opinion to the board of
directors of DoubleClick that, as of June 13, 1999, the share exchange ratio was
fair from a financial point of view to DoubleClick. Goldman Sachs subsequently
confirmed its oral opinion by delivery of its written opinion dated June 13,
1999.

    Goldman Sachs did not update its opinion to consider the impact
DoubleClick's merger with NetGravity will have on the fairness of the share
exchange ratio from a financial point of view to DoubleClick.

    The full text of the written opinion of Goldman Sachs, dated June 13, 1999,
which sets forth assumptions made, matters considered and limitations on the
review undertaken in connection with the opinion, is attached as APPENDIX D and
is incorporated by reference in this joint proxy statement/ prospectus. You
should read this opinion in its entirety.

    In connection with its opinion, Goldman Sachs reviewed, among other things,

    - the merger agreement;

    - the registration statement on Form S-1 relating to the initial public
      offering of DoubleClick common stock, including the prospectus therein
      dated February 20, 1998;

    - annual reports to stockholders and annual reports on Form 10-K of Abacus
      for the three years ended December 31, 1998;

    - annual report to stockholders and annual report on Form 10-K of
      DoubleClick for the one year ended December 31, 1998;

    - interim reports to stockholders and quarterly reports on Form 10-Q of
      Abacus and DoubleClick;

    - other communications from Abacus and DoubleClick to their stockholders;
      and

    - internal financial analyses and forecasts for Abacus and DoubleClick
      prepared by their managements, including operating synergies projected by
      the managements of Abacus and DoubleClick to result from the merger.

    Goldman Sachs also held discussions with members of the senior management of
Abacus and DoubleClick regarding the strategic rationale for, and the potential
benefits of, the merger and the past and current business operations, financial
condition and future prospects of their companies. In addition, Goldman Sachs:

    - reviewed the reported price and trading activity for the Abacus common
      stock and DoubleClick common stock;

    - compared financial and stock market information for Abacus and DoubleClick
      with similar information for other companies the securities of which are
      publicly traded;

    - reviewed the financial terms of recent business combinations in the
      Internet and direct marketing industries specifically and in other
      industries generally; and

    - performed other studies and analyses Goldman Sachs considered appropriate.

    Goldman Sachs relied upon the accuracy and completeness of all of the
financial and other information reviewed by it and assumed the accuracy and
completeness for purposes of rendering its opinion. Goldman Sachs did not make
an independent evaluation or appraisal of the assets and liabilities of Abacus
or DoubleClick or any of their subsidiaries and were not furnished with any
evaluation or appraisal. Goldman Sachs has assumed, with the consent of
DoubleClick's board of directors, that the merger will be

                                       33
<PAGE>
accounted for as a pooling of interests under generally accepted accounting
principles. The advisory services and opinion of Goldman Sachs were provided for
the information and assistance of the board of directors of DoubleClick in
connection with its consideration of the merger, and the opinion does not
constitute a recommendation as to how any holder of DoubleClick common stock
should vote with respect to the merger.

    DoubleClick and Abacus did not impose any material limitations on Goldman
Sachs in performing its financial analyses and investigations.

    The following is a summary of the material financial analyses used by
Goldman Sachs in connection with providing its opinion to DoubleClick's board of
directors on June 13, 1999. In providing its opinion, Goldman Sachs did not
assign any relative importance to any particular financial analysis.

    The following summaries of financial analyses include information presented
in tabular format. You should read these tables together with the text of each
summary.

    SHARE EXCHANGE RATIO HISTORY.  Goldman Sachs calculated the ratio of the
market price of Abacus common stock to the market price of DoubleClick common
stock on June 10, 1999 and the ratio of the average market price of Abacus
common stock to the average market price of DoubleClick common stock during
selected periods ending on June 10, 1999. The results are shown below:

<TABLE>
<CAPTION>
PERIOD                                                AVERAGE SHARE EXCHANGE RATIO
- ------                                                ----------------------------
<S>                                                   <C>
June 10, 1999 Closing Price                                        .813
10 days ending June 10, 1999                                       .788
30 days ending June 10, 1999                                       .726
60 days ending June 10, 1999                                       .699
90 days ending June 10, 1999                                       .891
1 Year ending June 10, 1999                                       2.073
</TABLE>

    PREMIUM ANALYSIS.  Goldman Sachs calculated the implied premium being paid
in the merger based on the ratio of the market price of Abacus common stock to
the market price of DoubleClick common stock on selected dates and the ratio of
the average market price of Abacus common stock to the average market price of
DoubleClick common stock during selected periods ending on June 11, 1999. The
results are shown below:

<TABLE>
<CAPTION>
                              IMPLIED PREMIUM
                                    AT
                                1.05 SHARE
    PRICE/AVERAGE PRICE       EXCHANGE RATIO
- ----------------------------  ---------------
<S>                           <C>
February 1, 1999                    11.3%
March 1, 1999                      (25.3)%
April 1, 1999                       22.5%
May 1, 1999                         75.2%
June 11, 1999                       25.1%
5 days ending June 11, 1999         30.4%
10 days ending June 11, 1999        32.0%
30 days ending June 11, 1999        44.9%
60 days ending June 11, 1999        55.8%
90 days ending June 11, 1999        35.0%
</TABLE>

    PUBLIC MARKET COMPARISON--DOUBLECLICK. Goldman Sachs reviewed and compared
selected financial information, ratios and multiples for DoubleClick to
corresponding financial information, ratios and public market multiples for six
publicly traded companies in the Internet advertising industry:

    - AdForce Inc.;

    - Flycast Communications Corp.;

                                       34
<PAGE>
    - InfoSpace.com Inc.;

    - Modem Media Poppe Tyson Inc.;

    - NetGravity, Inc.; and

    - 24/7 Media Inc.

    Goldman Sachs also reviewed and compared selected financial information,
ratios and multiples for DoubleClick to corresponding financial information,
ratios and public market multiples for six publicly traded companies in the
Internet infrastructure/services industry:

    - Broadvision Inc.;

    - Exodus Communications Inc.;

    - Inktomi Corp.;

    - Portal Software Inc.;

    - USWeb/CKS Corp.; and

    - Vignette Corp.

    The selected companies were chosen because they are publicly traded Internet
companies with operations that for purposes of analysis may be considered
similar to DoubleClick. The multiples and ratios were calculated using the
closing price for the common stock of DoubleClick and each of the selected
companies on June 11, 1999 and, except as otherwise indicated below, were based
on the most recent publicly available information. Goldman Sachs' analyses of
the selected companies compared the following to the results for DoubleClick:

    - closing share price on June 11, 1999 as a percentage of 52-week high share
      price;

    - the growth in revenues for the immediately preceding quarter as compared
      to the same quarter in the immediately preceding year;

    - equity market capitalization, which is the fully diluted market value of
      equity, as a multiple of annualized latest quarter revenues;

    - equity market capitalization as a multiple of annualized latest quarter
      gross profit;

    - equity market capitalization as a multiple of estimated revenue for
      calendar years 1999 and 2000 (based on Institutional Brokers Estimate
      System, or IBES, estimates); and

    - estimated five-year growth rate (provided by IBES).

                                       35
<PAGE>
    The results of these analyses are summarized as follows:

<TABLE>
<CAPTION>
                                                                 SELECTED PUBLICLY TRADED
                                                              INTERNET ADVERTISING COMPANIES
                                                     -------------------------------------------------
                  RATIO/MULTIPLE                         RANGE        MEDIAN      MEAN     DOUBLECLICK
- ---------------------------------------------------  -------------   --------   --------   -----------
<S>                                                  <C>             <C>        <C>        <C>
June 11, 1999 Closing Share Price as a Percentage
  of 52-Week High Share Price......................  36.3%-75.5%       57.5%      56.2%        51.7%

Growth Latest Quarter Revenue/Year Ago.............  12.5%-677.8%     128.3%     258.4%        69.8%

Equity Market Capitalization as a Multiple of
  Annualized Latest Quarter Revenue................  5.4x-62.3x        20.5x      25.0x        43.1x

Equity Market Capitalization as a Multiple of
  Annualized Latest Quarter Gross Profit...........  41.5x-85.9x       59.1x      61.4x        82.0x

Equity Market Capitalization as a Multiple of IBES
  1999 Estimated Revenue...........................  4.9x-40.5x        15.7x      20.4x        25.5x

Equity Market Capitalization as a Multiple of IBES
  2000 Estimated Revenue...........................  3.8x-23.6x         8.7x      12.0x        15.8x

IBES Estimated 5-Year Growth Rate..................  40.0%-65.0%       45.0%      45.0%        50.0%

<CAPTION>
                                                             SELECTED PUBLICLY TRADED INTERNET
                                                            INFRASTRUCTURE/ SERVICES COMPANIES
                                                     -------------------------------------------------
                  RATIO/MULTIPLE                         RANGE        MEDIAN      MEAN     DOUBLECLICK
- ---------------------------------------------------  -------------   --------   --------   -----------
<S>                                                  <C>             <C>        <C>        <C>
June 11, 1999 Closing Share Price as a Percentage
  of 52-Week High Share Price......................  51.4%-93.5%       71.9%      72.0%        51.7%

Growth Latest Quarter Revenue/Year Ago.............  83.2%-411.8%     290.5%     252.2%        69.8%

Equity Market Capitalization as a Multiple of
  Annualized Latest Quarter Revenue................  5.2x-81.7x        41.1x      44.0x        43.1x

Equity Market Capitalization as a Multiple of
  Annualized Latest Quarter Gross Profit...........  29.4x-273.0x      94.7x     112.7x        82.0x

Equity Market Capitalization as a Multiple of IBES
  1999 Estimated Revenue...........................  4.6x-58.3x        33.3x      33.4x        25.5x

Equity Market Capitalization as a Multiple of IBES
  2000 Estimated Revenue...........................  3.0x-41.5x        19.1x      20.8x        15.8x

IBES Estimated 5-Year Growth Rate..................  50.0%-75.0%       70.5%      65.1%        50.0%
</TABLE>

    PUBLIC MARKET COMPARISON--ABACUS. Goldman Sachs reviewed and compared
selected financial information, ratios and multiples for Abacus to corresponding
financial information, ratios and public market multiples for six publicly
traded large cap companies in the direct marketing industry:

    - Acxiom Corp.;

    - Equifax Inc.;

    - Great Universal Stores PLC;

    - Harte Hanks, Inc.;

    - Snyder Communications Inc.; and

    - VNU NV.

                                       36
<PAGE>
    Goldman Sachs also reviewed and compared selected financial information,
ratios and multiples for Abacus to corresponding financial information, ratios
and public market multiples for five publicly traded small cap/niche companies
in the direct marketing industry:

    - Advo Inc.;

    - Catalina Marketing Corp.;

    - Fair Isaac & Co. Inc.;

    - infoUSA Inc.; and

    - MemberWorks Inc.

    The selected companies were chosen because they are publicly traded direct
marketing companies with operations that for purposes of analysis may be
considered similar to Abacus. The multiples and ratios were calculated using the
closing price for the common stock of Abacus and each of the selected companies
on June 11, 1999 and, except as otherwise indicated below, were based on the
most recent publicly available information. Goldman Sachs' analyses of the
selected companies compared the following to the results for Abacus:

    - closing share price on June 11, 1999 as a percentage of 52-week high share
      price;

    - the ratio of the closing share price on June 11, 1999 to estimated
      earnings for calendar years 1999 and 2000 (based on estimates of Wall
      Street analysts);

    - estimated 5-year growth rate (provided by IBES);

    - the ratio of the closing share price on June 11, 1999 to estimated
      earnings for calendar year 1999 (based on estimates of Wall Street
      analysts) as a multiple of estimated 5-year growth rate (provided by
      IBES);

    - levered market capitalization, which is the fully diluted market value of
      equity plus the book value of debt less cash, as a multiple of last
      12 months sales;

    - levered market capitalization as a multiple of last 12 months earnings
      before interest, taxes, depreciation and amortization, or EBITDA;

    - levered market capitalization as a multiple of last 12 months earnings
      before interest and taxes, or EBIT; and

    - the ratio of total debt to capital.

                                       37
<PAGE>
    The results of these analyses are summarized as follows:

<TABLE>
<CAPTION>
                                                                     SELECTED PUBLICLY TRADED
                                                               LARGE CAP DIRECT MARKETING COMPANIES
                                                          ----------------------------------------------
                     RATIO/MULTIPLE                           RANGE        MEDIAN      MEAN      ABACUS
- --------------------------------------------------------  -------------   --------   --------   --------
<S>                                                       <C>             <C>        <C>        <C>
June 11, 1999 Closing Share Price as a Percentage of
  52-Week High Share Price..............................  49.6%-95.7%      78.7%      77.3%       86.1%

Closing Share Price on June 11, 1999 to Wall Street
  Analysts Estimated Earnings for Calendar Year 1999....  17.7x-29.4x      25.0x      24.6x       49.7x

Closing Share Price on June 11, 1999 to Wall Street
  Analysts Estimated Earnings for Calendar Year 2000....  13.4x-27.1x      21.7x      21.3x       35.3x

IBES Estimated 5-Year Growth Rate.......................  10.0%-35.0%      17.0%      19.8%       40.0%

Closing Share Price on June 11, 1999 to Wall Street
  Analysts Estimated Earnings for Calendar Year 1999 as
  a Multiple of IBES Estimated 5-year Growth Rate.......  0.5x-2.7x         1.3x       1.5x        1.2x

Levered Market Capitalization as a Multiple of Last 12
  Months Sales..........................................  2.0x-4.3x         3.3x       3.1x       15.4x

Levered Market Capitalization as a Multiple of Last 12
  Months EBITDA.........................................  11.0x-18.7x      13.6x      14.5x       37.5x

Levered Market Capitalization as a Multiple of Last 12
  Months EBIT...........................................  14.0x-31.1x      15.9x      18.7x       40.1x

Total Debt to Capital...................................  0.0%-81.6%       22.5%      30.2%        2.1%

<CAPTION>
                                                           SELECTED PUBLICLY TRADED SMALL CAP/NICHE DIRECT
                                                                         MARKETING COMPANIES
                                                          --------------------------------------------------
                     RATIO/MULTIPLE                           RANGE         MEDIAN       MEAN       ABACUS
- --------------------------------------------------------  --------------   ---------   ---------   ---------
<S>                                                       <C>              <C>         <C>         <C>
June 11, 1999 Closing Share Price as a Percentage of
  52-Week High Share Price..............................  39.8%-94.6%        77.0%       74.1%        86.1%

Closing Share Price on June 11, 1999 to Wall Street
  Analysts Estimated Earnings for Calendar Year 1999....  11.0x-57.1x        24.8x       27.8x        49.7x

Closing Share Price on June 11, 1999 to Wall Street
  Analysts Estimated Earnings for Calendar Year 2000....  9.7x-44.2x         21.5x       22.8x        35.3x

IBES Estimated 5-Year Growth Rate.......................  17.5%-40.0%        19.9%       22.7%        40.0%

Closing Share Price on June 11, 1999 to Wall Street
  Analysts Estimated Earnings for Calendar Year 1999 as
  a Multiple of IBES Estimated 5-year Growth Rate.......  0.6x-1.5x           1.3x        1.3x         1.2x

Levered Market Capitalization as a Multiple of Last 12
  Months Sales..........................................  0.6x-7.2x           3.1x        3.9x        15.4x

Levered Market Capitalization as a Multiple of Last 12
  Months EBITDA.........................................  4.6x-20.1x         13.2x       14.3x        37.5x

Levered Market Capitalization as a Multiple of Last 12
  Months EBIT...........................................  8.3x-29.0x         16.1x       19.8x        40.1x

Total Debt to Capital...................................  0.3%-160.7%        13.7%       33.0%         2.1%
</TABLE>

    In performing this public market comparison Goldman Sachs used those
operating statistics it considered most relevant for each of the two companies.
The operating statistics utilized in performing the public market comparison for
DoubleClick were those commonly utilized in analyzing Internet companies

                                       38
<PAGE>
and the operating statistics utilized in performing the public market comparison
for Abacus were those commonly utilized in analyzing direct marketing companies.

    In performing these analyses, Goldman Sachs did not assign relative
importance or weights to the various sets of ratios and multiples.

    CONTRIBUTION ANALYSIS.  Goldman Sachs compared Abacus and DoubleClick
stockholders' percentage ownership of the combined company following the merger
to the percentage contribution by Abacus and DoubleClick to the combined
company's 1999 and 2000 estimated system revenues, total revenues and gross
profit on a pro forma basis. The analysis did not take into account any
synergies that may result from the merger. Based on this analysis, DoubleClick
stockholders' percentage ownership of the combined company would equal or exceed
DoubleClick's percentage contribution to the combined company in each of 1999
and 2000. The results of this analysis are summarized as follows:

               Based on Wall Street Consensus Research Estimates
              for DoubleClick and Management Estimates for Abacus
            -------------------------------------------------------

<TABLE>
<CAPTION>
                                                                  % CONTRIBUTION
                                                               ABACUS    DOUBLECLICK
                                                              --------   -----------
<S>                                                           <C>        <C>
1.05 Exchange Ratio.........................................  20.5%          79.5%
1999 Estimated System Revenues*.............................  30.4%          69.6%
2000 Estimated System Revenues..............................  29.4%          70.6%
1999 Estimated Total Revenues...............................  37.8%          62.2%
2000 Estimated Total Revenues...............................  36.1%          63.9%
1999 Estimated Gross Profit.................................  48.5%          51.5%
2000 Estimated Gross Profit.................................  45.1%          54.9%
</TABLE>

- ------------------------

    *System revenues include revenues earned with respect to network sales
relating to publishers which are part of the DoubleClick Network, fees earned
from independent publishers and advertisers which use the DART technology to
deliver ad impressions, and amounts invoiced on behalf of Compaq Computer Corp,
in accordance with an advertising services agreement between Compaq and
DoubleClick. On June 29, 1999, Compaq agreed to transfer to CMGI, Inc. a
controlling interest in AltaVista. Compaq and its wholly owned subsidiary
Digital Equipment Corporation contributed the assets and liabilities comprising
AltaVista's business, which included the Advertising Services Agreement, to a
new company that CMGI owns approximately 83% of, with the remainder owned by
Compaq.

            Based on Management Estimates for DoubleClick and Abacus
            -------------------------------------------------------

<TABLE>
<CAPTION>
                                                                  % CONTRIBUTION
                                                               ABACUS    DOUBLECLICK
                                                              --------   -----------
<S>                                                           <C>        <C>
1.05 Exchange Ratio.........................................  20.5%          79.5%
1999 Estimated System Revenues..............................  25.2%          74.8%
2000 Estimated System Revenues..............................  20.3%          79.7%
1999 Estimated Total Revenues...............................  30.8%          69.2%
2000 Estimated Total Revenues...............................  23.5%          76.5%
1999 Estimated Gross Profit.................................  41.4%          58.6%
2000 Estimated Gross Profit.................................  31.6%          68.4%
</TABLE>

    PRO FORMA MERGER ANALYSIS.  Goldman Sachs prepared pro forma analyses of the
financial impact of the merger to DoubleClick stockholders both (A) using
management estimates for DoubleClick and Abacus and (B) using Wall Street
consensus research estimates for DoubleClick and management estimates for
Abacus.

                                       39
<PAGE>
    Goldman Sachs compared the 1998 earnings per share and 1999 and 2000
estimated earnings per share of DoubleClick common stock on a standalone basis
to the 1998 earnings per share and 1999 and 2000 estimated earnings per share of
the common stock of the combined company on a pro forma basis. In performing
this analysis Goldman Sachs included DoubleClick and Abacus managements'
estimates of the potential synergies to be realized following the merger. Based
on these analyses, the merger would be accretive to stockholders of DoubleClick
on an earnings per share basis in each of 1999 and 2000.

    The results of this analysis are summarized as follows:

<TABLE>
<CAPTION>
                                                                                BASED ON ABACUS
                                                            BASED ON ABACUS     MANAGEMENT AND
                                                             MANAGEMENT AND       DOUBLECLICK
                                                              DOUBLECLICK        MANAGEMENT'S
                                                            STREET ESTIMATES       ESTIMATES
                                                            ----------------   -----------------
<S>                                                         <C>                <C>
1998 Earnings Per Share Accretion.........................       $0.58               $0.58
1999 Estimated Earnings Per Share Accretion...............       $0.47               $0.47
2000 Estimated Earnings Per Share Accretion...............       $0.43               $0.48
</TABLE>

    For each of the years 1999 and 2000, Goldman Sachs also compared the
estimated revenue per share of DoubleClick common stock on a pre-merger basis to
the estimated revenue per share of the common stock of the combined company on a
pro forma basis. In performing this analysis, Goldman Sachs included DoubleClick
and Abacus managements' estimates of the potential synergies that may be
realized following the merger. The results of this analysis are summarized as
follows:

<TABLE>
<CAPTION>
                                                            BASED ON ABACUS      BASED ON ABACUS
                                                             MANAGEMENT AND       MANAGEMENT AND
                                                              DOUBLECLICK          DOUBLECLICK
                                                            STREET ESTIMATES   MANAGEMENT ESTIMATES
                                                            ----------------   --------------------
<S>                                                         <C>                <C>
1999 % Accretion..........................................         14.4%                6.5%
2000 % Accretion..........................................         18.4%                3.2%
</TABLE>

    SELECTED TRANSACTION ANALYSIS--INTERNET. Goldman Sachs compared information
for nine selected transactions in the Internet industry to similar information
for the proposed merger, including:

    - the premium of the aggregate levered consideration, which is the
      consideration paid by DoubleClick plus the book value of Abacus's debt,
      less cash, over the closing market value of the acquired company;

    - aggregate levered consideration as a multiple of last 12 months sales;

    - aggregate levered consideration as a multiple of last 12 months gross
      margin;

    - aggregate levered consideration as a multiple of next 12 months estimated
      sales (provided by Wall Street analysts); and

    - aggregate levered consideration as a multiple of next 12 months estimated
      gross margin (provided by Wall Street analysts).

    The results of the analyses are summarized as follows:

<TABLE>
<CAPTION>
                                                           SELECTED TRANSACTIONS IN
                                                            THE INTERNET INDUSTRY
                                                      ----------------------------------   DOUBLECLICK
RATIO/MULTIPLE                                           RANGE        MEDIAN      MEAN       /ABACUS
- --------------                                        ------------   --------   --------   -----------
<S>                                                   <C>            <C>        <C>        <C>
Premium to Market...................................  -4.2%-67.4%     45.8%       37.7%       25.1%
Aggregate Levered Consideration as a Multiple of
  Last 12 Months Sales..............................  0.9x-255.2x     12.9x       60.2x       19.3x
Aggregate Levered Consideration as a Multiple of
  Last 12 Months Gross Margin.......................  10.1x-971.1x    53.0x      320.3x       24.4x
Aggregate Levered Consideration as a Multiple of
  Next 12 Months Sales Estimated by Wall Street
  Analysts..........................................  0.2x-143.6x     16.1x       47.3x       12.0x
Aggregate Levered Consideration as a Multiple of
  Next 12 Months Gross Margin Estimated by Wall
  Street Analysts...................................  0.7x-395.7x     17.3x       77.7x       15.1x
</TABLE>

                                       40
<PAGE>
    In performing this analysis, Goldman Sachs did not assign relative
importance or weights to the various sets of ratios and multiples.

    SELECTED TRANSACTION ANALYSIS--DIRECT MARKETING. Goldman Sachs compared
information for ten selected transactions in the direct marketing industry to
similar information for the proposed merger, including:

    - the premium of the aggregate levered consideration over the closing market
      value of the acquired company;

    - aggregate levered consideration as a multiple of last 12 months sales;

    - aggregate levered consideration as a multiple of last 12 months EBIT;

    - aggregate levered consideration as a multiple of last 12 months EBITDA;

    - aggregate levered consideration as a multiple of next 12 months estimated
      sales (provided by Wall Street analysts); and

    - aggregate levered consideration as a multiple of next 12 months estimated
      EBIT (provided by Wall Street analysts).

<TABLE>
<CAPTION>
                                                            SELECTED TRANSACTIONS
                                                                IN THE DIRECT
                                                              MARKETING INDUSTRY
                                                      ----------------------------------   DOUBLECLICK
RATIO/MULTIPLE                                           RANGE        MEDIAN      MEAN       /ABACUS
- --------------                                        ------------   --------   --------   -----------
<S>                                                   <C>            <C>        <C>        <C>
Premium to Market...................................    0.0%-69.1%    21.6%      18.9%        25.1%
Aggregate Levered Consideration as a Multiple of
  Last 12 Months Sales..............................     1.7x-6.2x     3.2x       2.7x        19.3x
Aggregate Levered Consideration as a Multiple of
  Last 12 Months EBITDA.............................    9.6x-39.2x    18.5x      13.8x        47.1x
Aggregate Levered Consideration as a Multiple of
  Last 12 Months EBIT...............................  11.1x-107.2x    29.2x      19.6x        51.8x
Aggregate Levered Consideration as a Multiple of
  Next 12 Months Sales Estimated by Wall Street
  Analysts..........................................     1.4x-7.0x     3.6x       3.0x        12.0x
Aggregate Levered Consideration as a Multiple of
  Next 12 Months EBIT Estimated by Wall Street
  Analysts..........................................   10.8x-36.5x    19.2x      14.7x        32.3x
</TABLE>

    In performing this analysis, Goldman Sachs did not assign relative
importance or weights to the various sets of ratios and multiples.

    IMPLIED MULTIPLE ANALYSIS. Goldman Sachs calculated the aggregate levered
consideration proposed in the merger, based on an exchange ratio of 1.05 and the
market price of Abacus common stock on June 11, 1999, as a multiple of Abacus's
estimated system revenues, total revenues, gross profit, operating income and
net income in the years 1999 and 2000, and compared the results to DoubleClick's
trading multiples.

                                       41
<PAGE>
Goldman Sachs based its analysis on management estimates for Abacus and Wall
Street consensus research estimates for DoubleClick. The results of this
analysis are summarized as follows:

<TABLE>
<CAPTION>
                                                            ABACUS    DOUBLECLICK
                                                           --------   -----------
<S>                                                        <C>        <C>
MULTIPLES OF SYSTEM REVENUES
  1999E..................................................   14.9x        23.8x
  2000E..................................................   10.1x        15.3x
MULTIPLES OF TOTAL REVENUES
  1999E..................................................   14.9x        33.4x
  2000E..................................................   10.1x        21.4x
MULTIPLES OF GROSS PROFIT
  1999E..................................................   18.7x        64.1x
  2000E..................................................   13.1x        39.2x
MULTIPLES OF OPERATING INCOME
  1999E..................................................   39.8x           NM
  2000E..................................................   28.2x           NM
MULTIPLES OF NET INCOME
  1999E..................................................   63.2x           NM
  2000E..................................................   44.7x           NM
</TABLE>

    The preparation of a fairness opinion is a complex process and is not
necessarily susceptible to partial analysis or summary description. Selecting
portions of the analyses or of the summary set forth above, without considering
the analyses as a whole, could create an incomplete view of the processes
underlying Goldman Sachs' opinion. In arriving at its fairness determination,
Goldman Sachs considered the results of all the analyses it performed. No
company or transaction used in the above analyses as a comparison is directly
comparable to DoubleClick or Abacus or the contemplated merger.

    The analyses were prepared for purposes of providing an opinion to the
DoubleClick board of directors as to the fairness from a financial point of view
to DoubleClick of the share exchange ratio. The analyses do not purport to be
appraisals or necessarily reflect the prices at which businesses or securities
actually may be sold. Analyses based upon forecasts of future results are not
necessarily indicative of actual future results, which may be significantly more
or less favorable than suggested by the analyses. The analyses underlying the
Goldman Sachs opinion are inherently subject to uncertainty, being based upon
numerous factors or events beyond the control of the parties or their respective
advisors.

    As described above, Goldman Sachs' opinion to DoubleClick's board of
directors was one of many factors taken into consideration by DoubleClick's
board of directors in making its determination to approve the merger. The
foregoing is a summary of the material financial analyses used by Goldman Sachs
in connection with providing its opinion but it does not purport to be a
complete description of the analyses performed by Goldman Sachs.

    Goldman Sachs, as part of its investment banking business, is continually
engaged in the valuation of businesses and their securities in connection with
mergers and acquisitions, negotiated underwritings, competitive biddings,
secondary distributions of listed and unlisted securities, private placements
and valuations for estate, corporate and other purposes. Goldman Sachs is
familiar with DoubleClick having provided investment banking services to
DoubleClick from time to time, including having acted as managing underwriter of
the initial public offering of DoubleClick common stock in February 1998 and a
subsequent public offering of DoubleClick common stock in December 1998, and
having acted as its financial advisor in connection with, and having
participated in the negotiations leading to, the merger agreement. Goldman Sachs
provides a full range of financial advisory and securities services and, in the
course of its normal trading activities, may from time to time effect
transactions and hold securities, including derivative securities, of
DoubleClick or Abacus for its own account and for the accounts of customers.

    Under a letter agreement dated May 26, 1999, DoubleClick engaged Goldman
Sachs to act as its financial advisor in connection with the possible
acquisition by DoubleClick or any of its affiliates of all or

                                       42
<PAGE>
a portion of the stock or assets of Abacus. According to the terms of this
letter agreement, DoubleClick has agreed to pay Goldman Sachs a transaction fee
based on the outcome of the merger as follows:

    - if the merger is consummated, Goldman Sachs will receive a transaction fee
      of $7.0 million; or

    - if the merger is not consummated and in accordance with the merger
      agreement DoubleClick receives a payment in connection with the
      termination of the merger agreement or the failure to consummate the
      merger, Goldman Sachs will receive a termination fee of $3.5 million.

    DoubleClick also has agreed to reimburse Goldman Sachs for their reasonable
out-of-pocket expenses, including attorneys' fees, and to indemnify Goldman
Sachs against certain liabilities, including liabilities arising under the
federal securities laws.

    ABACUS

    Under an engagement letter dated February 15, 1999, Abacus engaged
BancBoston Robertson Stephens Inc. to render an opinion as to the fairness of
the exchange ratio, from a financial point of view, to holders of shares of
Abacus common stock (other than DoubleClick or any of its affiliates).

    BancBoston Robertson Stephens did not update its opinion to consider the
impact DoubleClick's merger with NetGravity will have on the fairness of the
share exchange ratio from a financial point of view to Abacus stockholders.

    On June 13, 1999 at a meeting of the Abacus board held to evaluate the
proposed merger, BancBoston Robertson Stephens delivered to the Abacus board its
written opinion that, as of June 13, 1999 and based on the assumptions made, the
matters considered and the limitations on the review undertaken described in the
opinion, the exchange ratio was fair from a financial point of view to holders
of shares of Abacus common stock (other than DoubleClick or any of its
affiliates). No limitations were imposed by DoubleClick or the Abacus board on
BancBoston Robertson Stephens with respect to the investigations made or
procedures followed by it in furnishing its opinion. The exchange ratio was
determined through negotiations between the managements of Abacus and
DoubleClick. Although BancBoston Robertson Stephens did assist the management of
Abacus in those negotiations, it was not asked by, and did not recommend to,
Abacus that any specific exchange ratio constituted the appropriate exchange
ratio for the merger. BancBoston Robertson Stephens also assisted Abacus'
management in the negotiations leading to an agreement on principal structural
terms of the merger.

    The full text of the BancBoston Robertson Stephens opinion, which sets
forth, among other things, assumptions made, matters considered and limitations
on the review undertaken, is attached as APPENDIX E and is incorporated in this
joint prospectus/proxy statement by reference. BancBoston Robertson Stephens
prepared its opinion for the benefit and use of the Abacus board in its
consideration of the merger; the opinion does not constitute a recommendation to
Abacus stockholders as to how they should vote or take any other action with
respect to the merger. BancBoston Robertson Stephens has consented to the use of
its opinion in this joint proxy statement/prospectus. We urge Abacus
stockholders to read the opinion in its entirety.

    The BancBoston Robertson Stephens opinion does not address:

    - the relative merits of the merger and the other business strategies that
      the Abacus board has considered or may be considering; or

    - the underlying business decision of the Abacus board to proceed with the
      merger.

    The summary of the BancBoston Robertson Stephens opinion set forth in this
joint proxy statement/ prospectus is qualified in its entirety by reference to
the full text of the opinion.

    In preparing their opinion, BancBoston Robertson Stephens, among other
things:

    - reviewed publicly available financial statements and other business and
      financial information of Abacus and DoubleClick;

                                       43
<PAGE>
    - reviewed internal financial statements and other financial and operating
      data about Abacus and DoubleClick prepared by the managements of Abacus
      and DoubleClick;

    - reviewed financial forecasts and other forward looking financial
      information relating to Abacus and DoubleClick prepared by the managements
      of Abacus and DoubleClick;

    - reviewed with Abacus and DoubleClick the publicly available consensus
      estimates of research analysts relating to Abacus and DoubleClick;

    - held discussions with the managements of Abacus and DoubleClick concerning
      the businesses, past and current operations, financial condition and
      future prospects of Abacus and DoubleClick, independently and combined,
      cost savings and other synergies that are expected to result from the
      merger, and management views of the strategic rationale for the merger;

    - reviewed the financial terms and conditions in the merger agreement;

    - reviewed the stock price and trading history of Abacus and DoubleClick;

    - compared the financial performance of Abacus and DoubleClick and the
      prices and trading activity of Abacus common stock and DoubleClick common
      stock with that of other publicly traded companies comparable with Abacus
      and DoubleClick;

    - compared the financial terms of the merger with the financial terms, to
      the extent publicly available, of other transactions it deemed relevant;

    - reviewed the pro forma impact of the merger on DoubleClick's net revenue
      per share;

    - reviewed and considered information prepared by members of management of
      Abacus and DoubleClick relating to the relative contributions of Abacus
      and DoubleClick to the combined company;

    - prepared a discounted cash flow analysis of Abacus;

    - participated in discussions and negotiations among representatives of
      Abacus and DoubleClick and their financial and legal advisors; and

    - made other studies and inquiries, and reviewed other data, as it deemed
      relevant.

    In its review and analysis, and in arriving at its opinion, BancBoston
Robertson Stephens assumed and relied upon the accuracy and completeness of all
of the financial and other information provided to it (including information
furnished to it orally or otherwise discussed with it by management of Abacus
and DoubleClick) or publicly available and neither attempted to verify, nor
assumed responsibility for verifying, any of this information. BancBoston
Robertson Stephens relied upon the assurances of management of Abacus and
DoubleClick that they were not aware of any facts that would make this
information inaccurate or misleading. Furthermore, BancBoston Robertson Stephens
did not obtain or make, or assume any responsibility for obtaining or making,
any independent evaluation or appraisal of the properties, assets or liabilities
(contingent or otherwise) of Abacus or DoubleClick, nor was BancBoston Robertson
Stephens furnished with any evaluation or appraisal.

    With respect to the financial forecasts and projections (and the underlying
assumptions and bases, including synergies related to the merger) for each of
Abacus and DoubleClick that BancBoston Robertson Stephens reviewed, upon the
advice of the managements of Abacus and DoubleClick, BancBoston Robertson
Stephens assumed that these forecasts and projections:

    - had been reasonably prepared in good faith on the basis of reasonable
      assumptions;

    - reflected the best available estimates and judgments as to the future
      financial condition and performance of Abacus and DoubleClick; and

    - will be realized in the amounts and in the time periods estimated.

                                       44
<PAGE>
    In this regard, BancBoston Robertson Stephens noted that each of Abacus and
DoubleClick face exposure to the Year 2000 problem. BancBoston Robertson
Stephens did not undertake any independent analysis to evaluate the reliability
or accuracy of the assumptions made by the managements of Abacus and DoubleClick
with respect to the potential effect that the Year 2000 problem might have on
their forecasts.

    In addition, BancBoston Robertson Stephens assumed that:

    - the merger will be consummated upon the terms set forth in the merger
      agreement without material alteration, including, among other things, that
      the merger will be accounted for as a "pooling of interests" business
      combination in accordance with U.S. generally accepted accounting
      principles;

    - the merger will be treated as a tax-free reorganization as defined in the
      Internal Revenue Code of 1986, as amended; and

    - the historical financial statements of Abacus and DoubleClick reviewed by
      it had been prepared and fairly presented in accordance with U.S.
      generally accepted accounting principles consistently applied.

    BancBoston Robertson Stephens relied as to all legal matters relevant to
rendering its opinion on the advice of counsel.

    Although developments following the date of the BancBoston Robertson
Stephens opinion may affect the opinion, BancBoston Robertson Stephens assumed
no obligation to update, revise or reaffirm its opinion. The BancBoston
Robertson Stephens opinion is necessarily based upon market, economic and other
conditions as in effect on, and information made available to BancBoston
Robertson Stephens as of, the date of the BancBoston Robertson Stephens opinion.
It should be understood that subsequent developments may affect the conclusion
expressed in the BancBoston Robertson Stephens opinion and that BancBoston
Robertson Stephens disclaims any undertaking or obligation to advise any person
of any change in any matter affecting the opinion which may come or be brought
to its attention after the date of the opinion. The BancBoston Robertson
Stephens opinion is limited to the fairness, from a financial point of view and
as of the date thereof, of the exchange ratio to holders of shares of Abacus
common stock (other than DoubleClick or any of its affiliates). BancBoston
Robertson Stephens does not express any opinion as to:

    - the value of any employee agreement or other arrangement entered into in
      connection with the merger;

    - any tax or other consequences that might result from the merger; or

    - what the value of DoubleClick common stock will be when issued to Abacus's
      stockholders in the merger or the price at which the shares of DoubleClick
      common stock that are issued in the merger may be traded in the future.

    The following is a summary of the material financial analyses performed by
BancBoston Robertson Stephens in connection with rendering the BancBoston
Robertson Stephens opinion. The summary of the financial analyses is not a
complete description of all of the analyses performed by BancBoston Robertson
Stephens. Some of the information in this section is presented in a tabular
form. IN ORDER TO BETTER UNDERSTAND THE FINANCIAL ANALYSES PERFORMED BY
BANCBOSTON ROBERTSON STEPHENS, THESE TABLES MUST BE READ TOGETHER WITH THE TEXT
OF EACH SUMMARY. THE BANCBOSTON ROBERTSON STEPHENS OPINION IS BASED UPON THE
TOTALITY OF THE VARIOUS ANALYSES WHICH IT PERFORMED, AND NO PARTICULAR PORTION
OF THE ANALYSIS HAS ANY MERIT STANDING ALONE.

                                       45
<PAGE>
    In its financial analysis, BancBoston Robertson Stephens used the following
consensus estimates of financial analysis ("consensus street estimates") for
Abacus and DoubleClick:

<TABLE>
<CAPTION>
                                                   ABACUS              DOUBLECLICK
                                             -------------------   -------------------
                                               1999       2000       1999       2000
                                             --------   --------   --------   --------
<S>                                          <C>        <C>        <C>        <C>
Net Revenue................................   $65.9      $89.5      $103.9     $164.4
EBIT.......................................    25.1       34.4       (23.1)      (4.6)
Net Income.................................    16.0       27.2       (17.7)      (0.6)
EPS........................................   $1.53      $2.08      $(0.44)    $(0.01)
</TABLE>

    As explained above, BancBoston Robertson Stephens, upon the advice of the
managements of Abacus and DoubleClick, assumed, for purposes of its opinion,
that such forecasts reflected the best available estimates and judgments as to
the future financial condition and performance of Abacus and DoubleClick and
that such forecasts will be realized. However, because forecasts of this type
are based upon a number of significant uncertainties and contingencies, most of
which are difficult to predict and beyond the control of Abacus and DoubleClick,
neither Abacus nor DoubleClick can make any assurances that any of such
forecasts of financial analysts will be realized.

    EXCHANGE RATIO AND IMPLIED PREMIUM ANALYSIS.  BancBoston Robertson Stephens
compared the historical ratios of the average closing price of Abacus common
stock to the average closing price of DoubleClick common stock over various
periods ending June 11, 1999. The following table sets forth the ratios of the
average closing prices of Abacus common stock compared to DoubleClick common
stock for the various periods ending June 11, 1999 and the implied premium
(discount) of the exchange ratio to the average ratios.

<TABLE>
<CAPTION>
                               RATIO OF AVERAGE CLOSING PRICES       PREMIUM (DISCOUNT)
                               OF ABACUS COMMON STOCK COMPARED   OF EXCHANGE RATIO IN MERGER
PERIOD ENDING JUNE 11, 1999      TO DOUBLECLICK COMMON STOCK       TO PERIOD AVERAGE RATIO
- ----------------------------   -------------------------------   ---------------------------
<S>                            <C>                               <C>
        10 days                             0.796x                            31.9%
        30 days                             0.729x                            44.1%
        60 days                             0.702x                            49.5%
        90 days                             0.893x                            17.5%
 Preceding twelve months                    2.075x                           (49.4)%
</TABLE>

    COMPARABLE COMPANIES ANALYSIS.  Using publicly available information,
BancBoston Robertson Stephens analyzed, among other things, the equity value and
trading multiples of Abacus and selected publicly traded companies that have
similar business and operating profiles, including:

    - Acxiom Corp.

    - ADVO, Inc.

    - Harte-Hanks, Inc.

    - InfoUSA, Inc.

    - M/A/R/C Group

    - Snyder Communications, Inc.

    Multiples compared by BancBoston Robertson Stephens included aggregate value
(equity value plus debt, less cash) to estimated earnings before interest and
taxes ("EBIT") for calendar years 1999 and 2000, price to earnings per share for
calendar years 1999 and 2000 and EBIT and price/earnings to the five-year
earnings per share growth rate for calendar year 2000. All multiples were based
on closing stock prices as of June 11, 1999 and the consensus street estimates
for Abacus.

                                       46
<PAGE>
    Using the ranges of multiples set forth below, the following Abacus equity
values, Abacus values per share and exchange ratios are implied:

<TABLE>
<CAPTION>
                                              IMPLIED ABACUS EQUITY VALUE
                                                    ($ IN MILLIONS)           MEAN IMPLIED      MEAN IMPLIED
                                              ----------------------------    ABACUS EQUITY    EXCHANGE RATIO
                           MULTIPLE RANGE           RANGE           MEAN     VALUE PER SHARE        (A)
                          -----------------   -----------------   --------   ---------------   --------------
<S>                       <C>                 <C>                 <C>        <C>               <C>
2000 EBIT                    9.0x-14.0x       $ 334.4-$506.5      $  420.5       $ 39.06           0.440
1999 EBIT                    12.0x-18.0x      $ 325.6-$476.1      $  400.9       $ 37.24           0.419
2000 P/E                    15.0x - 25.0x     $ 333.1-$555.2      $  444.1       $ 41.26           0.465
1999 P/E                    20.0x - 30.0x     $ 319.1-$478.7      $  398.9       $ 37.06           0.417
2000 EBIT Multiple/
  Growth Rate               0.40x - 0.60x     $ 550.6-$825.9      $  688.3       $ 63.94           0.720
2000 P/E/Growth Rate        0.80x - 1.10x     $ 710.6-$977.1      $  843.9       $ 78.39           0.883
Mean (b)                                                                         $ 54.91           0.618
</TABLE>

- ------------------------

(a) Based on the closing price of DoubleClick common stock on June 11, 1999 of
    $88.81.

(b) Based on the average of the mean of EBIT and P/E methodologies and the mean
    of EBIT and P/E to growth rate methodologies.

                                       47
<PAGE>
    BancBoston Robertson Stephens also reviewed multiples for the comparable
companies of aggregate value to LTM, 1999 and 2000 revenues, but BancBoston
Robertson Stephens believed that the revenue multiples of the comparable
companies were not as relevant as the EBIT and P/E multiples that it considered
because Abacus generally has higher operating margins than the comparable
companies. The revenue multiples generally implied a lower valuation for Abacus
than the EBIT and P/E multiples that BancBoston Robertson Stephens considered.
BancBoston Robertson Stephens also reviewed multiples for the comparable
companies of aggregate value to LTM EBIT and LTM P/E, but BancBoston Robertson
Stephens believed that the EBIT and P/E multiples based on historical LTM
results were not as relevant as the forward 1999 and 2000 EBIT and P/E
multiples. The LTM multiples generally implied a lower valuation for Abacus than
the forward 1999 and 2000 multiples that BancBoston Robertson Stephens
considered.

    CONTROL PREMIUM ANALYSIS.  Based upon its review of the range of premiums to
the acquired company's closing market price 30 days prior to the announcement of
the transaction that have been paid in the precedent transactions listed below,
BancBoston Robertson Stephens applied a range of control premiums of 25.0% to
60.0% (with a mean of 42.5%) to the mean equity valuation implied by the
foregoing comparable companies analysis. The results of this analysis are
summarized below:

<TABLE>
<CAPTION>
                                       IMPLIED ABACUS EQUITY VALUE
                                             ($ IN MILLIONS)           MEAN IMPLIED
                                       ----------------------------    ABACUS EQUITY      MEAN IMPLIED
                                             RANGE           MEAN     VALUE PER SHARE   EXCHANGE RATIO(A)
                                       -----------------   --------   ---------------   -----------------
<S>                                    <C>                 <C>        <C>               <C>
2000 EBIT                              $   525.6-$ 672.7   $  599.1       $ 55.66             0.627
1999 EBIT                              $   501.1-$ 641.4   $  571.2       $ 53.06             0.597
2000 P/E                               $   555.2-$ 710.6   $  632.9       $ 58.79             0.662
1999 P/E                               $   498.6-$ 638.3   $  568.5       $ 52.81             0.595
2000 EBIT Multiple/Growth Rate         $  860.4-$1,101.3   $  980.8       $ 91.11             1.026
2000 P/E/Growth Rate                   $1,054.8-$1,350.2   $1,202.5       $111.71             1.258
    Mean (b)                                                              $ 78.25             0.881
</TABLE>

- ------------------------

(a) Based on the closing price of DoubleClick common stock on June 11, 1999 of
    $88.81.

(b) Based on the average of the mean of EBIT and P/E methodologies and the mean
    of EBIT and P/E to growth rate methodologies

    PRECEDENT TRANSACTION ANALYSIS.  Using publicly available information,
BancBoston Robertson Stephens analyzed the implied transaction value multiples
paid or proposed to be paid in selected acquisition transactions in the database
marketing services industry and the Internet content and services industry,
including:

    Database Marketing Services Industry

    - Fingerhut Cos./Federated Dept. Stores (February 11, 1999)

    - Pharmaceutical Marketing/Quintiles Transnational (December 15, 1998)

    - May & Speh/Acxiom (May 27, 1998)

    - Metromail/Great Universal Stores (March 13, 1998)

    - Direct Marketing Technology/Great Universal Stores (April 14, 1997)

    - Brann Holdings/Snyder Communications (March 19, 1997)

    - American List Corp./Snyder Communications (March 19, 1997)

    - Donnelley Marketing/First Data Corporation (September 5, 1996)

    Internet Content and Services Industry

    - TeleB@nc Financial/E*Trade (June 1, 1999)

                                       48
<PAGE>
    - Broadcast.com/Yahoo! (April 1, 1999)

    - Geocities/Yahoo! (January 28, 1999)

    - Excite/@Home (January 19, 1999)

    - Netscape/AOL (November 24, 1998)

    - N2K/CDnow (October 23, 1998)

    - CKS Group, Inc./USWeb Corporation (September 2, 1998)

    In analyzing these "precedent transactions," BancBoston Robertson Stephens
compared, among other things, the equity value in the transactions as a multiple
of net income for the preceeding twelve months ("LTM"), the aggregate value
(equity value plus debt less cash) as a multiple of calendar year 2000 estimated
revenues and the premiums paid to market prices in such transactions. All
multiples for the precedent transactions were based on public information
available at the time of the announcement. Based on this information and other
publicly available information, the following tables illustrate implied Abacus
equity valuations, Abacus equity valuations per share and exchange ratios
derived from applying a range of multiples that BancBoston Robertson Stephens
derived from the precedent transactions of LTM net income and of calendar year
2000 revenue. BancBoston Robertson Stephens applied different multiples for the
transactions in the database marketing services industry and the Internet
content and services industry because companies in these industries generally
have different operating and trading profiles and, therefore, are generally
valued in the public equity markets according to different trading multiples.

<TABLE>
<CAPTION>
                                                                     IMPLIED ABACUS EQUITY
                                                 MULTIPLE/                   VALUE                                   MEAN
                                                PERCENTAGE              ($ IN MILLIONS)           MEAN IMPLIED     IMPLIED
                                            -------------------   ----------------------------    ABACUS EQUITY    EXCHANGE
                                             RANGE       MEAN           RANGE           MEAN     VALUE PER SHARE   RATIO(A)
                                            --------   --------   -----------------   --------   ---------------   --------
<S>                                         <C>        <C>        <C>                 <C>        <C>               <C>

Database Marketing Services:
  Equity Value/LTM Net Income               30.0x-     35.0x      $ 360.2-$ 480.2     $  420.2       $ 39.04        0.440
                                            40.0x

  One Day Premium to Abacus Closing         20.0%-     25.0%      $ 963.2-$1,043.4    $1,003.3       $ 93.20        1.049
    Price(b)                                30.0%

  One Month Premium to Abacus Closing       25.0%-     30.0%      $1,076.2-$1,162.3   $1,119.3       $103.98        1.171
    Price(c)                                35.0%
      Mean                                                                                           $ 78.74        0.887

Internet Content and Services Industry:
  Aggregate Value/CY 2000 Revenue(d)        10.0x-     12.5x      $ 919.5-$1,366.9    $1,143.2       $106.20        1.196
                                            15.0x

  One Day Premium to Abacus Closing         30.0%-     35.0%      $1,043.4-$1,123.7   $1,083.6       $100.66        1.133
    Price(b)                                40.0%

  One Month Premium to Abacus Closing       50.0%-     55.0%      $1,291.5-$1,377.6   $1,334.5       $123.97        1.396
    Price(c)                                60.0%
      Mean                                                                                           $110.28        1.242
</TABLE>

- ------------------------

(a) Based on the closing price of DoubleClick common stock on June 11, 1999 of
    $88.81.

(b) Based on the closing price of Abacus common stock on June 11, 1999 of
    $74.56. Premium paid based upon the closing price of the common stock of the
    target company one day prior to the announcement of each transaction.

(c) Based on the closing price of Abacus common stock one month prior to
    announcement of the merger. Premium paid based upon the closing price of the
    common stock of the target company one month prior to the announcement of
    each transaction.

(d) Aggregate value means equity value plus debt less cash.

    Using a weighting of 15% of the mean implied equity value per share and
exchange ratio for the Internet content and services industry and 85% for the
database marketing services industry, implied an

                                       49
<PAGE>
equity value per share of $83.47 and an exchange ratio of 0.940. BancBoston
Robertson Stephens applied this relative weighting based upon its analyses that
approximately 15% of Abacus' pro forma revenues in the year 2000 would be
derived from Internet activities and approximately 85% of such revenues would be
derived from its database marketing operations.

    No company, business or transaction compared in the comparable companies
analysis or precedent transaction analysis is identical to Abacus or
DoubleClick. Accordingly, an analysis of the results of the foregoing is not
entirely mathematical; rather it involves complex considerations and judgments
concerning differences in financial and operating characteristics and other
factors that could affect the acquisition, public trading and other values of
the comparable companies, precedent transactions or the business segment,
company or transactions to which they are being compared.

    DISCOUNTED CASH FLOW ANALYSIS.  BancBoston Robertson Stephens performed a
discounted cash flow analysis of the after-tax free cash flows of Abacus for
calendar years 1999 through 2003 using financial analyst consensus earnings
estimates and a net revenue growth rate for years 2001 to 2003 based on
conversations with Abacus management. BancBoston Robertson Stephens first
discounted the projected, after-tax free cash flows through December 31, 2003
using discount rates ranging from 12.5% to 15.5%. Abacus after-tax free
cash-flows were calculated as the after-tax operating earnings of Abacus
adjusted to add back non-cash expenses and deduct uses of cash not reflected in
the income statement. The range of discount rates used reflect BancBoston
Robertson Stephens' judgment as to the approximate weighted average cost of
capital for Abacus. BancBoston Robertson Stephens then added to the present
value of the cash flows the terminal value of Abacus at December 31, 2003,
discounted back at the same discount rate to represent a present value. The
terminal value was computed by multiplying the projected EBIT for Abacus in
calendar year 2003 by terminal multiples ranging from 14.0x to 18.0x. The range
of terminal multiples selected reflect BancBoston Robertson Stephens' judgment
as to an appropriate range of multiples at the end of the reference period,
based upon its review of trading multiples for comparable companies. The
following table summarizes the resulting implied equity valuations, equity
values per share and exchange ratios using a terminal value multiple of 16.0x,
which was the median of the range applied by BancBoston Robertson Stephens:

<TABLE>
<CAPTION>
                                                                                                  MEAN
                                        IMPLIED EQUITY VALUATION             MEAN IMPLIED       IMPLIED
                                 --------------------------------------   ABACUS EQUITY VALUE   EXCHANGE
DISCOUNT RATES                           RANGE                MEAN             PER SHARE        RATIO(A)
- --------------                   ---------------------   --------------   -------------------   --------
<S>                              <C>                     <C>              <C>                   <C>
12.5%-15.5%                      $783.4-$869.6 million   $825.0 million         $76.64           0.863
</TABLE>

- ------------------------

(a) Based on the closing price of DoubleClick common stock on June 11, 1999 of
    $88.81.

    RELATIVE CONTRIBUTION ANALYSIS.  Based upon the consensus street estimates
for Abacus and DoubleClick, BancBoston Robertson Stephens analyzed the
contributions of Abacus and DoubleClick to the gross revenue, net revenue and
gross profit of the combined company for the last twelve months and calendar
years 1999 and 2000. In conducting this analysis, BancBoston Robertson Stephens
discounted the gross revenue, net revenue and gross profit of Abacus for these
periods by 62.2%, which reflected the discount between DoubleClick's calendar
year 2000 revenue multiple of 23.5x (defined as the DoubleClick stock trading
price as of June 11, 1999 divided by estimated calendar year 2000 revenue per
share) and Abacus's calendar year 2000 revenue multiple of 8.9x.

                                       50
<PAGE>
    The results of this analysis are set forth below:

<TABLE>
<CAPTION>
                                                                         IMPLIED ABACUS      IMPLIED
                                                      IMPLIED ABACUS    EQUITY VALUE PER     EXCHANGE
                             ABACUS    DOUBLECLICK   EQUITY VALUATION        SHARE          RATIO (A)
                            --------   -----------   ----------------   ----------------   ------------
<S>                         <C>        <C>           <C>                <C>                <C>
Gross Revenue:
2000......................     12.6%        87.4%     $  507 million        $ 51.26           0.577
1999......................     14.3%        85.7%     $  584 million        $ 59.13           0.666
LTM.......................     16.3%        83.7%     $  682 million        $ 69.05           0.778

Net Revenue:
2000......................     17.1%        82.9%     $  721 million        $ 72.96           0.822
1999......................     19.3%        80.7%     $  840 million        $ 84.99           0.957
LTM.......................     17.7%        82.3%     $  751 million        $ 76.02           0.856

Gross Profit:
2000......................     22.8%        77.2%     $1,036 million        $104.84           1.181

Mean:.....................                                                                    0.834
</TABLE>

- ------------------------

(a) Based on the closing price of DoubleClick common stock on June 11, 1999 of
    $88.81.

    BancBoston Robertson Stephens also analyzed the contributions of Abacus and
DoubleClick to the gross revenue, net revenue and gross profit of the combined
company for the last twelve months and calendar years 1999 and 2000 by
discounting Abacus gross revenue, net revenue and gross profit for these periods
by 38.6%, which reflected the discount between DoubleClick's calendar year 2000
net revenue growth rate of 58.3% and Abacus's calendar year 2000 net revenue
growth rate of 35.8%.

    The results of this analysis are set forth below:

<TABLE>
<CAPTION>
                                                                         IMPLIED ABACUS      IMPLIED
                                                      IMPLIED ABACUS    EQUITY VALUE PER     EXCHANGE
                             ABACUS    DOUBLECLICK   EQUITY VALUATION        SHARE          RATIO (A)
                            --------   -----------   ----------------   ----------------   ------------
<S>                         <C>        <C>           <C>                <C>                <C>
Gross Revenue:
2000......................     19.0%        81.0%     $  821 million        $ 83.09           0.936
1999......................     21.3%        78.7%     $  947 million        $ 95.82           1.079
LTM.......................     24.0%        76.0%     $1,106 million        $111.87           1.260

Net Revenue:
2000......................     25.0%        75.0%     $1,168 million        $118.20           1.331
1999......................     28.0%        72.0%     $1,360 million        $137.65           1.550
LTM.......................     25.8%        74.2%     $1,217 million        $123.14           1.387

Gross Profit:
2000......................     32.5%        67.5%     $1,678 million        $169.74           1.911

Mean:.....................                                                                    1.350
</TABLE>

- ------------------------

(a) Based on the closing price of DoubleClick common stock on June 11, 1999 of
    $88.81.

    In considering these analyses, BancBoston Robertson Stephens noted that
Abacus stockholders would own approximately 20.5% of the fully diluted shares of
DoubleClick immediately after consummation of the merger. BancBoston Robertson
Stephens also noted that the exchange ratio of 1.05x represented a 4% discount
to the average of the means implied by the relative contribution analyses.

                                       51
<PAGE>
    PRELIMINARY DOUBLECLICK VALUATION.

    STOCK VOLATILITY ANALYSIS.  BancBoston Robertson Stephens noted that the
stock of Internet companies generally trade with greater volatility than the
Abacus common stock. Since Abacus' other potential strategic partners would most
likely be Internet companies, BancBoston Robertson Stephens compared the
volatility of DoubleClick common stock with the volatility of shares of selected
Internet companies. BancBoston Robertson Stephens analyzed the volatility of
DoubleClick common stock and the common stock of selected publicly traded
Internet companies over various periods ending June 11, 1999. The selected
companies included Amazon.com, @Home, E*Trade, Ebay and CNet.

    BancBoston Robertson Stephens noted that over various trading day periods
ended June 11, 1999, the volatility of the common stock of the above companies
ranged from 86.4% to 152.4%, while the volatility of DoubleClick common stock
ranged from 76.4% to 148.4% over the same periods. BancBoston Robertson Stephens
also noted that while the volatility of DoubleClick common stock was comparable
to the volatility of the stock of other Internet companies, the volatility of
DoubleClick common stock was approximately twice as much as the volatility of
Abacus common stock.

    REVENUE MULTIPLE ANALYSIS OF INTERNET MARKET LEADERS VS. MARKET
FOLLOWERS.  Using consensus street estimates for DoubleClick, BancBoston
Robertson Stephens analyzed estimated calendar year 2000 revenue multiples
(defined as the stock trading price as of June 11, 1999 divided by estimated
calendar year 2000 revenue per share) for DoubleClick and selected publicly
traded companies, comparing the calendar year 2000 revenue multiples for several
categories of Internet market leaders and their market followers, including
Internet access providers (AOL, leader; Mindspring, follower), portals (Yahoo!,
leader; Lycos, follower), business-to-business e-commerce (Vertical Net, leader;
Earthweb, follower) and online targeted marketing (DoubleClick, leader; 24/7
Media, follower). BancBoston Robertson Stephens noted that the multiple spread
factor (defined as the calendar year 2000 revenue multiple for the category
leader divided by the calendar year 2000 revenue multiple for the category
follower) was 3.9x for the Internet access providers, 3.6x for the portals, 5.2x
for the business-to-business e-commerce providers and 4.8x for the online
targeted marketing companies. Applying a range of multiple spread factors of
3.5x-5.5x to 24/7 Media's calendar year 2000 revenue multiple of 4.9x and
DoubleClick's estimated calendar year 2000 revenue per share implied a range of
DoubleClick share prices of $65.32 to $102.64.

    DISCOUNTED EQUITY VALUE ANALYSIS.  Using consensus street estimates of
DoubleClick's net revenue in calendar year 2000, BancBoston Robertson Stephens
calculated an implied DoubleClick equity valuation per share by applying
calendar year 2000 revenue multiples of 25.0x to 40.0x to these net revenue
estimates. The revenue multiples used were derived from a review by BancBoston
Robertson Stephens of comparable revenue multiples for the Internet market
leaders. BancBoston Robertson Stephens then calculated the net present value of
the valuations by applying discount rates ranging from 15% to 25%. This range of
discount rates were based upon BancBoston Robertson Stephens' review of discount
rates applied to comparable companies, adjusted to reflect the greater
volatility of DoubleClick common stock and DoubleClick's higher growth rate.
This analysis implied DoubleClick share prices ranging from $71.89 to $131.83.

    A similar analysis based upon consensus street estimates of DoubleClick's
net revenue in calendar year 2001 and revenue multiples of 15.0x to 25.0x
implied DoubleClick share prices ranging from $64.00 to $122.52.

    PRO FORMA ANALYSES.  Using consensus street estimates for Abacus and
DoubleClick, BancBoston Robertson Stephens analyzed pro forma effects resulting
from the merger, including, among other things,

                                       52
<PAGE>
the impact of the merger on the projected net revenues per share of the combined
company for fiscal years 1999 and 2000. The following table summarizes the
results of this analysis:

     Fiscal year 1999 estimated net revenue per share accretion      27.4%

     Fiscal year 2000 estimated net revenue per share accretion      22.3%

    The actual results achieved by the combined company may vary from projected
results and the variations may be material.

    REVENUE ACCRETION SENSITIVITY ANALYSIS.  BancBoston Robertson Stephens also
analyzed the impact of a range of potential revenue synergies on the pro forma
revenues per share of the resulting combined company for fiscal year 2000. The
following table summarizes the results of this analysis:

<TABLE>
<CAPTION>
                                                      FY2000 REVENUE PER
                          FY2000E REVENUE SYNERGIES    SHARE ACCRETION
                          -------------------------   ------------------
<S>                       <C>                         <C>
Exchange Ratio of 1.050x  $0.00--$30.00 million         22.3%--36.7%
</TABLE>

    OTHER FACTORS AND COMPARATIVE ANALYSES.  In rendering its opinion,
BancBoston Robertson Stephens considered other factors and conducted other
comparative analyses, including, among other things a review of the history of
trading prices and volume for DoubleClick common stock and Abacus common stock,
for the period from June 11, 1998 to June 11, 1999.

    While the foregoing summary describes the analyses and factors that
BancBoston Robertson Stephens deemed material in its presentation to the Abacus
board, it is not a comprehensive description of all analyses and factors
considered by BancBoston Robertson Stephens. The preparation of a fairness
opinion is a complex process that involves various determinations as to the most
appropriate and relevant methods of financial analysis and the application of
these methods to the particular circumstances and, therefore, this opinion is
not readily susceptible to summary description. BancBoston Robertson Stephens
believes that its analyses must be considered as a whole and that selecting
portions of its analyses and of the factors considered by it, without
considering all analyses and factors, would create an incomplete view of the
evaluation process underlying the BancBoston Robertson Stephens opinion. Several
analytical methodologies were employed and no one method of analysis should be
regarded as critical to the overall conclusion reached by BancBoston Robertson
Stephens. Each analytical technique has inherent strengths and weaknesses, and
the nature of the available information may further affect the value of
particular techniques. The conclusions reached by BancBoston Robertson Stephens
are based on all analyses and factors taken as a whole and also on application
of BancBoston Robertson Stephens' own experience and judgment. These conclusions
may involve significant elements of subjective judgment and qualitative
analysis. BancBoston Robertson Stephens therefore gives no opinion as to the
value or merit standing alone of any one or more parts of the analysis it
performed. In performing its analyses, BancBoston Robertson Stephens considered
general economic, market and financial conditions and other matters, many of
which are beyond the control of Abacus and DoubleClick. The analyses performed
by BancBoston Robertson Stephens are not necessarily indicative of actual values
or future results, which may be significantly more or less favorable than those
suggested by these analyses. Accordingly, analyses relating to the value of a
business do not purport to be appraisals or to reflect the prices at which the
business actually may be purchased. Furthermore, no opinion is being expressed
as to the prices at which shares of DoubleClick common stock or Abacus common
stock may be traded at any future time.

                                       53
<PAGE>
    The engagement letter between BancBoston Robertson Stephens and Abacus
provides that, for its services, BancBoston Robertson Stephens is entitled to
receive a transaction fee equal to 0.55% of the aggregate transaction value
payable upon completion of the merger and a fee of $1.0 million payable upon
delivery of the BancBoston Robertson Stephens opinion, which fee shall be
credited against the transaction fee. Abacus has also agreed to reimburse
BancBoston Robertson Stephens for its out-of-pocket expenses, including legal
fees, and to indemnify and hold harmless BancBoston Robertson Stephens and its
affiliates and any director, employee or agent of BancBoston Robertson Stephens
or any of its affiliates, or any person controlling BancBoston Robertson
Stephens or its affiliates for losses, claims, damages, expenses and liabilities
relating to or arising out of services provided by BancBoston Robertson Stephens
as financial advisor to Abacus. The terms of the fee arrangement with BancBoston
Robertson Stephens, which Abacus and BancBoston Robertson Stephens believe are
customary in transactions of this nature, were negotiated at arm's length
between Abacus and BancBoston Robertson Stephens, and the Abacus board was aware
of these fee arrangements, including the fact that a significant portion of the
fees payable to BancBoston Robertson Stephens is contingent upon completion of
the merger. BancBoston Robertson Stephens has provided investment banking
services to Abacus for which it has been paid fees, including acting as lead
manager for Abacus's initial public offering. BancBoston Robertson Stephens
maintains a market in the shares of Abacus common stock and DoubleClick common
stock. In the ordinary course of its business, BancBoston Robertson Stephens may
trade in Abacus's securities or DoubleClick's securities for its own account and
the account of its customers and, accordingly, may at any time hold a long or
short position in Abacus's securities or DoubleClick's securities.

    BancBoston Robertson Stephens was retained based on BancBoston Robertson
Stephens' experience as a financial advisor in connection with mergers and
acquisitions and in securities valuations generally, as well as BancBoston
Robertson Stephens' investment banking relationship and familiarity with Abacus.

    BancBoston Robertson Stephens is an internationally recognized investment
banking firm. As part of its investment banking business, BancBoston Robertson
Stephens is frequently engaged in the valuation of businesses and their
securities in connection with mergers and acquisitions, negotiated
underwritings, secondary distributions of securities, private placements and
other purposes.

INTERESTS OF ABACUS'S OFFICERS AND DIRECTORS IN THE MERGER

    When considering the recommendation of the Abacus board, Abacus stockholders
should be aware that Abacus's officers and directors have interests in the
merger that differ from, or are in addition to, those of Abacus stockholders.
The Abacus board was aware of these potential conflicts and considered them.

    As of October 11, 1999, Abacus's executive officers and directors held
options to purchase a total of 984,902 shares of Abacus common stock, at
exercise prices ranging from $1.32 to $71.75 per share, of which 638,447 shares
are unvested options to purchase common stock. The options granted to
M. Anthony White, Daniel C. Synder and Carlos E. Sala provide for accelerated
vesting of options upon a change in control. If the merger were to occur on
October 11, 1999, options held by these persons to purchase an aggregate of
438,915 shares of Abacus common stock, at exercise prices ranging from $1.32 to
$44.06 per share, would vest in connection with the merger. Under the terms of
the options granted to Frank Kenny, Antony H. Lee and Robert L. North, options
to purchase an aggregate of 48,532 shares of Abacus common stock, at exercise
prices ranging from $21.75 to $71.75 per share, will automatically become
immediately exercisable if the merger is completed.

                                       54
<PAGE>
    Upon completion of the merger, the vesting under stock options held by the
following officers and directors of Abacus will accelerate as set forth below:

<TABLE>
<CAPTION>
                                                                                               WEIGHTED
                                                                                               AVERAGE
                                                                                   OPTIONS     EXERCISE
NAME                                          POSITION WITH ABACUS               ACCELERATED    PRICE
- ----                             ----------------------------------------------  -----------   --------
<S>                              <C>                                             <C>           <C>
M. Anthony White                 Chairman of the Board, Chief Executive Officer    122,200      $26.71
                                 and Director
Daniel C. Snyder                 Director, President--Emerging Markets and         126,465       12.05
                                 Chairman--Abacus Direct Europe
Carlos E. Sala                   Senior Vice President--Finance, Chief             190,250       29.65
                                 Financial Officer, Treasurer and Secretary
Frank Kenny                      Director                                           16,844       52.40
Antony H. Lee                    Director                                           17,844       51.35
Robert L. North                  Director                                           13,844       58.72
</TABLE>

    M. Anthony White, Daniel C. Snyder, Carlos E. Sala and Christopher M. Dice
have employment agreements with Abacus entitling them to, among other things,
severance payments equal to two times their annual salary and performance
bonuses if their employment is terminated upon a change of control. Brian Rainey
has an employment agreement with Abacus entitling him to, among other things,
severance payments equal to his annual salary if his employment is terminated
upon a change of control.

    Upon completion of the merger, DoubleClick and Abacus will enter into
employment agreements with each of the following officers of Abacus: M. Anthony
White, Daniel C. Snyder, Carlos E. Sala, Christopher M. Dice and Brian M.
Rainey.

These agreements provide for the following annual base salaries:

<TABLE>
<CAPTION>
NAME                                                          BASE SALARY
- ----                                                          -----------
<S>                                                           <C>
M. Anthony White............................................    $363,000
Daniel C. Snyder............................................     225,000
Carlos E. Sala..............................................     278,300
Christopher M. Dice.........................................     225,000
Brian M. Rainey.............................................     165,000
</TABLE>

These agreements also provide that these officers, other than Mr. Rainey, are
eligible for annual incentive compensation, in an amount not in excess of 100%
of their base salary, as determined by the compensation committee of the
DoubleClick board. Mr. Rainey's agreement provides that he is eligible to
receive incentive compensation and sales commissions each year as determined by
the DoubleClick board. Incentive compensation decisions for these officers will
be based upon the accomplishment of annual business-related performance goals
for the combined company. See "The Merger Agreement and Related
Agreements--Related Agreements."

    The merger agreement provides that, from and after the effective time,
DoubleClick will cause Abacus to indemnify the present and former officers,
directors and employees and agents of Abacus in respect of acts or omissions
occurring on or prior to the effective time. This indemnity will apply to the
full extent permitted under the Abacus certificate of incorporation or the
Abacus bylaws in each case as in effect on the date of the merger agreement, for
a period of six years. See "The Merger Agreement and Related
Agreements--Director and Officer Indemnification and Insurance."

    DoubleClick has agreed to expand its board and to nominate M. Anthony White,
the Chairman and Chief Executive Officer of Abacus, to be a director.

    As a result, these directors and executive officers may be more likely to
vote to approve the merger than Abacus stockholders generally.

                                       55
<PAGE>
APPLICABLE WAITING PERIODS AND REGULATORY APPROVALS

    The merger is subject to U.S. antitrust laws. We have made the required
filings with the Department of Justice and the Federal Trade Commission. We are
not, however, permitted to complete the merger until the applicable waiting
period has expired or terminated. The applicable waiting expired on August 20,
1999. The Department of Justice and the Federal Trade Commission, as well as a
state or private person, may challenge the merger at any time before or after
its completion.

    Neither Abacus nor DoubleClick is aware of any other material governmental
or regulatory approval required for completion of the merger, other than
compliance with applicable corporate law of Delaware.

MATERIAL FEDERAL INCOME TAX CONSIDERATIONS

    We have received the opinion of Parker Chapin Flattau & Klimpl, LLP, counsel
to Abacus, that, subject to the assumptions, exceptions, limitations and
qualifications set forth in their opinion (attached hereto as Exhibit 8.1) the
material United States federal income tax considerations relevant to the
exchange of shares of Abacus common stock for DoubleClick common stock in the
merger that are generally applicable to holders of Abacus common stock are as
follows:

A. The merger will constitute a reorganization within the meaning of the Code.

B.  A holder of Abacus common stock will not recognize any gain or loss solely
    upon such holder's receipt of DoubleClick common stock in exchange for such
    holder's Abacus common stock in the merger, except to the extent the holder
    of Abacus common stock receives cash in lieu of a fractional share of
    DoubleClick common stock.

C.  The aggregate tax basis of the DoubleClick common stock that a holder of
    Abacus common stock receives in the merger will be the same as the aggregate
    tax basis of the Abacus common stock surrendered by such holder in exchange
    for DoubleClick common stock (reduced by any tax basis attributable to any
    fractional share the holder is deemed to have disposed of).

D. The holding period of the DoubleClick common stock that each holder receives
    in the merger will include the period for which the Abacus common stock
    surrendered in exchange for DoubleClick common stock was considered to be
    held, if the surrendered Abacus common stock is held as a capital asset at
    the time of the merger.

E.  Cash payments that a holder of Abacus common stock receives in lieu of a
    fractional share will be treated as if the fractional share of DoubleClick
    common stock had been issued in the merger and then redeemed by DoubleClick.
    A holder of Abacus common stock receiving cash will recognize gain or loss
    upon payment measured by any difference between the amount of cash received
    and the holder's basis in the fractional share.

    The opinion of Parker Chapin Flattau & Kimpl, LLP and this discussion are
based on currently existing provisions of the Internal Revenue Code, existing
and proposed treasury regulations thereunder and current administrative rulings
and court decisions, all of which are subject to change. Any change, which may
or may not be retroactive, could alter the tax consequences to Abacus
stockholders as described above.

    Abacus stockholders should be aware that this discussion does not deal with
all federal income tax considerations that may be relevant to particular Abacus
stockholders in light of their particular circumstances, such as stockholders
who:

    - are dealers in securities;

    - are subject to the alternative minimum tax provisions of the Internal
      Revenue Code;

    - are foreign persons;

                                       56
<PAGE>
    - do not hold their Abacus common stock as capital assets; or

    - acquired their shares in connection with stock option or stock purchase
      plans or in other compensatory transactions.

    In addition, the following discussion does not address:

    - the tax consequences of the merger under foreign, state or local tax laws,
      or

    - the tax consequences of the assumption by DoubleClick of Abacus stock
      options or the tax consequences of the receipt of rights to acquire
      DoubleClick common stock. ACCORDINGLY, ABACUS STOCKHOLDERS ARE URGED TO
      CONSULT THEIR OWN TAX ADVISORS AS TO THE SPECIFIC TAX CONSEQUENCES TO THEM
      OF THE MERGER, INCLUDING THE APPLICABLE FEDERAL, STATE, LOCAL AND FOREIGN
      TAX CONSEQUENCES.

    The parties are not requesting and will not request a ruling from the
Internal Revenue Service as to the tax consequences of the merger. The
consummation of the merger is conditioned on DoubleClick's receiving an opinion
from Brobeck, Phleger & Harrison LLP and Abacus's receiving an opinion from
Parker Chapin Flattau & Klimpl, LLP in each case dated on the date of the
closing to the effect that the merger will constitute a reorganization within
the meaning of the Internal Revenue Code and the tax consequences to the Abacus
stockholders are as described above. Abacus stockholders should be aware that
the tax opinions do not bind the IRS. The IRS may therefore successfully assert
a contrary opinion. The tax opinions will be subject to assumptions and
qualifications, including but not limited to the truth and accuracy of
representations made by DoubleClick and Abacus.

    A successful IRS challenge to the reorganization status of the merger would
result in an Abacus stockholder recognizing taxable gain or loss with respect to
each share of Abacus common stock surrendered equal to the difference between
(A) each stockholder's basis in the share and (B) the fair market value, as of
the effective time, of the DoubleClick common stock received in exchange. In
this event, a stockholder's aggregate basis in the DoubleClick common stock
received would equal its fair market value as of the closing date of the merger,
and the stockholder's holding period for DoubleClick common stock would begin
the day after the merger.

    The acceleration of the vesting of options upon the merger for
Messrs. White, Snyder, Sala, Kenny Lee and North, together with any other
payments contingent upon or made in connection with the merger to
Messrs. White, Snyder, Sala, Kenny, Lee and North, may result in "excess
parachute payments" as defined in Section 280G of the Internal Revenue Code.
Excess parachute payments are not deductible in accordance with Section 280G. As
a result, DoubleClick will not be entitled to a tax deduction for the amounts
determined to be excess parachute payments. The amount of the lost deduction
will depend upon the value of the shares at the time of the merger and the
number of option shares being accelerated.

ANTICIPATED ACCOUNTING TREATMENT

    We intend to account for the merger as a pooling of interests for financial
reporting purposes in accordance with generally accepted accounting principles,
which means that Abacus and DoubleClick will be treated as if they had
previously been combined for accounting and financial reporting purposes. It is
a condition to completion of the merger that the independent auditors for
DoubleClick and Abacus, PricewaterhouseCoopers LLP, concur with DoubleClick
management's and Abacus management's conclusions as to the appropriateness of
pooling-of-interests accounting for the merger under APB No. 16, and the related
interpretations of the American Institute of Certified Public Accountants, the
Financial Accounting Standards Board and the rules and regulations of the
Commission. Under the pooling-of-interests method of accounting, each of the
parties' historical recorded assets and liabilities will be carried forward to
the combined company at their recorded amounts. In addition, the operating
results of the combined company will include both parties' operating results for
the entire fiscal year in which the merger is completed and the parties'
historical reported operating results for prior periods will be combined and
restated as the operating results of the combined company.

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NO APPRAISAL RIGHTS

    Stockholders of Abacus and DoubleClick are not entitled to exercise
dissenters' or appraisal rights as a result of the merger or to demand cash
payment for their shares under Delaware law.

DELISTING AND DEREGISTRATION OF ABACUS'S COMMON STOCK FOLLOWING THE MERGER

    If the merger is consummated, Abacus's common stock will be delisted from
The Nasdaq National Market and will be deregistered under the Securities
Exchange Act of 1934.

LISTING OF DOUBLECLICK COMMON STOCK TO BE ISSUED IN THE MERGER

    The filing of an application with the Nasdaq National Market for the listing
of the shares of DoubleClick common stock to be issued in the merger and the
shares of DoubleClick common stock to be reserved for issuance in connection
with the assumption of outstanding Abacus stock options is a condition to the
consummation of the merger.

RESTRICTIONS ON SALE OF SHARES BY AFFILIATES OF DOUBLECLICK AND ABACUS

    The shares of DoubleClick common stock to be issued in connection with the
merger will be registered under the Securities Act and will be freely
transferable under the Securities Act, except for shares of DoubleClick common
stock issued to any person who is deemed to be an affiliate of either
DoubleClick or Abacus at the time of the special meetings. Persons who may be
deemed to be affiliates include individuals or entities that control, are
controlled by, or are under common control of either DoubleClick or Abacus and
may include some of the officers, directors, or principal stockholders of
DoubleClick or Abacus. Affiliates may not sell their shares of DoubleClick
common stock acquired in connection with the merger except under:

    - an effective registration statement under the Securities Act covering the
      resale of those shares;

    - an exemption under paragraph (d) of Rule 145 under the Securities Act; or

    - another applicable exemption under the Securities Act.

    DoubleClick's registration statement on Form S-4, of which this joint proxy
statement/prospectus forms a part, does not cover the resale of shares of
DoubleClick common stock to be received by affiliates in the merger.

OPERATIONS FOLLOWING THE MERGER

    Following the merger, Abacus will operate as a division of DoubleClick.
DoubleClick intends to expand its board and to nominate M. Anthony White, the
Chairman and Chief Executive Officer of Abacus, to the board. The stockholders
of Abacus will become stockholders of DoubleClick, and their rights as
stockholders will be governed by DoubleClick's certificate of incorporation,
DoubleClick's bylaws and the laws of the State of Delaware.

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                              THE MERGER AGREEMENT
                             AND RELATED AGREEMENTS

    THE FOLLOWING IS A BRIEF SUMMARY OF THE MATERIAL PROVISIONS OF THE MERGER
AGREEMENT, A COPY OF WHICH IS ATTACHED AS APPENDIX A TO THIS JOINT PROXY
STATEMENT/PROSPECTUS AND INCORPORATED BY REFERENCE IN THIS JOINT PROXY
STATEMENT/PROSPECTUS. WE URGE YOU TO READ THE MERGER AGREEMENT IN ITS ENTIRETY
FOR A MORE COMPLETE DESCRIPTION OF THE MERGER. IN THE EVENT OF ANY DISCREPANCY
BETWEEN THE TERMS OF THE MERGER AGREEMENT OR OTHER AGREEMENTS AND THE FOLLOWING
SUMMARY, THE APPLICABLE AGREEMENT WILL CONTROL.

THE MERGER

    Abacus will merge with Atlanta Merger Corp., a wholly owned subsidiary of
DoubleClick, following

    - the approval and adoption of the merger agreement and the merger by the
      Abacus stockholders;

    - the approval of the issuance of DoubleClick common stock in the merger by
      the DoubleClick stockholders; and

    - the satisfaction or waiver of the other conditions to the merger.

    Abacus will be the surviving corporation and become a wholly owned
subsidiary of DoubleClick following the merger.

EFFECTIVE TIME

    As soon as practicable on or after the closing of the merger, the parties
will cause the merger to become effective by filing a certificate of merger with
the Secretary of State of the State of Delaware. DoubleClick and Abacus are
working toward completing the merger as soon as possible and hope to complete
the merger in the fall of 1999. Because the merger is subject to governmental
and other regulatory approvals, however, we cannot predict the exact timing.

CONVERSION OF ABACUS SHARES IN THE MERGER

    At the effective time, each outstanding share of Abacus common stock will
automatically be converted into the right to receive 1.05 shares of DoubleClick
common stock. The number of shares of DoubleClick common stock issuable in the
merger will be proportionately adjusted as appropriate

    - for any stock split, stock dividend or similar event with respect to
      Abacus common stock or DoubleClick common stock effected between the date
      of this joint proxy statement/prospectus and the completion of the merger;
      or

    - if prior to the completion of the merger, the number of shares of Abacus
      common stock on a fully diluted basis exceeds the number disclosed by
      Abacus to DoubleClick as of the date of the merger agreement.

ABACUS STOCK OPTION AND STOCK INCENTIVE PLANS

    At the effective time, each outstanding option to purchase shares of Abacus
common stock issued under Abacus's 1999 Stock Incentive Plan, Amended and
Restated 1996 Stock Incentive Plan, as amended, and Amended and Restated 1989
Stock Option Plan will be assumed by DoubleClick regardless of whether the
options are exercisable. Each Abacus stock option, which will be assumed by
DoubleClick, will continue to have the same terms, and be subject to the same
conditions, that were applicable to the option immediately prior to the
effective time, except that:

    - each Abacus stock option will be exercisable for shares of DoubleClick
      common stock;

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    - the number of shares of DoubleClick common stock issuable upon exercise of
      any given Abacus option will be determined by multiplying 1.05 by the
      number of shares of Abacus common stock underlying the option, rounded
      down to the nearest whole number; and

    - the per share exercise price of any given option will be determined by
      dividing the exercise price of the option immediately prior to the
      effective time by 1.05, rounded up to the nearest whole cent.

    The parties intend for the Abacus stock options assumed by DoubleClick to
qualify as incentive stock options to the extent the stock options qualified as
incentive stock options prior to the effective time. Stock options held by
non-employee directors will expire 90 days after the effective time.

NO FRACTIONAL SHARES

    No fractional shares of DoubleClick common stock will be issued in
connection with the merger. Instead Abacus stockholders will receive an amount
of cash, in lieu of a fraction of a share of DoubleClick common stock, equal to
(A) the product of this fraction multiplied by (B) the closing price for a share
of DoubleClick common stock on the Nasdaq National Market on the last business
day prior to the effective time.

THE EXCHANGE AGENT

    DoubleClick is required to deposit with a bank or trust company promptly
after the effective time, certificates representing the shares of DoubleClick
common stock to be exchanged for shares of Abacus common stock and cash to pay
for fractional shares and any dividends or distributions that holders of Abacus
common stock may be entitled to receive under the merger agreement.

EXCHANGE OF ABACUS STOCK CERTIFICATES FOR DOUBLECLICK STOCK CERTIFICATES

    Promptly after the effective time, the exchange agent will mail to Abacus
stockholders a letter of transmittal and instructions for surrendering their
Abacus stock certificates in exchange for DoubleClick stock certificates and
cash in lieu of fractional shares.

    ABACUS STOCKHOLDERS SHOULD NOT SUBMIT THEIR STOCK CERTIFICATES FOR EXCHANGE
UNTIL THEY HAVE RECEIVED THE LETTER OF TRANSMITTAL AND INSTRUCTIONS REFERRED TO
ABOVE.

    DOUBLECLICK STOCKHOLDERS SHOULD NOT SUBMIT THEIR STOCK CERTIFICATES FOR
EXCHANGE.

DISTRIBUTIONS WITH RESPECT TO UNEXCHANGED SHARES

    DoubleClick will issue a DoubleClick stock certificate or a check in lieu of
a fractional share in a name other than the name registered for the surrendered
Abacus stock certificate ONLY if the exchange agent is given all documents
required

    - to show and effect the unrecorded transfer of ownership; and

    - to show that any applicable stock transfer taxes have been paid.

    Abacus stockholders are not entitled to receive any dividends or other
distributions on DoubleClick common stock with a record date after the merger is
completed until they have surrendered their Abacus stock certificates in
exchange for DoubleClick stock certificates.

    If there is any dividend or other distribution on DoubleClick common stock
with a record date after the merger, former Abacus stockholders will receive,
only following surrender of their Abacus stock certificates, the dividend or
other distribution payable with respect to the whole shares of DoubleClick
common stock issued in exchange for their Abacus stock certificates.

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REPRESENTATIONS AND WARRANTIES

    DoubleClick and Abacus each made a number of representations and warranties
in the merger agreement about their authority to enter into the merger agreement
and to consummate the other transactions contemplated by the merger agreement
and about aspects of their business, financial condition, structure and other
facts pertinent to the merger.

    Abacus made representations about the following topics:

    - Abacus's organization, qualification to do business and good standing;

    - Abacus's capitalization;

    - Abacus's corporate power to enter into and its authorization of the merger
      agreement, the option agreement and the transactions contemplated by the
      merger agreement;

    - the effect of the merger agreement, option agreement and the merger on
      obligations of Abacus;

    - Abacus's possession of consents and permits required in connection with
      the merger agreement and transactions contemplated by the merger
      agreement;

    - possession of and compliance with permits required to conduct Abacus's
      business;

    - Abacus's compliance with applicable laws, rules and regulations of
      governmental entities;

    - Abacus's filings and reports with the Securities and Exchange Commission;

    - Abacus's financial statements;

    - changes in Abacus's business since December 31, 1998;

    - Abacus's employee benefit plans;

    - matters relating to Abacus's employees;

    - the treatment of the merger as a pooling of interests and as a tax-free
      reorganization;

    - Abacus's material contracts and obligations;

    - litigation involving Abacus;

    - environmental laws that apply to Abacus;

    - intellectual property used or owned by Abacus;

    - the effect of the Year 2000 on Abacus's business, products and services;

    - Abacus's taxes;

    - Abacus's insurance;

    - Abacus's title to the properties it owns and leases;

    - Abacus's affiliates;

    - Abacus's financial advisors;

    - Abacus's brokers' and finders' fees in connection with the merger;

    - Abacus's political contributions;

    - the inapplicability of the Delaware anti-takeover statute to the merger;
      and

    - restrictions on Abacus's business.

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    DoubleClick made representations about the following topics:

    - DoubleClick's organization, qualification to do business and good
      standing;

    - validity of DoubleClick's organizational documents;

    - DoubleClick's capitalization;

    - DoubleClick's corporate power to enter into and its authorization of the
      merger agreement and the transactions contemplated by the merger
      agreement;

    - the effect of the merger agreement and the merger on obligations of
      DoubleClick;

    - DoubleClick's possession of consents and permits required in connection
      with the merger agreement and transactions contemplated by the merger
      agreement;

    - DoubleClick's filings and reports with the Securities and Exchange
      Commission;

    - DoubleClick's financial statements;

    - the treatment of the merger as a pooling of interests and a tax-free
      reorganization;

    - DoubleClick's financial advisor;

    - DoubleClick's brokers' and finders' fees in connection with the merger;

    - DoubleClick's affiliates; and

    - absence of a material adverse effect since December 31, 1998.

    The representations and warranties in the merger agreement are complicated
and not easily summarized. We urge stockholders to read carefully the articles
in the merger agreement entitled "Representations and Warranties of Company" and
"Representations and Warranties of Parent."

ABACUS'S CONDUCT OF BUSINESS BEFORE COMPLETION OF THE MERGER

    Abacus has agreed that, until the completion of the merger or unless
DoubleClick consents in writing, Abacus and its subsidiaries will conduct their
businesses in the ordinary course of business consistent with past practices and
shall use reasonable efforts:

    - to keep available the services of their current officers, significant
      employees and consultants; and

    - to preserve their relationships with corporate partners, customers,
      suppliers and other persons with which they have significant business
      relations in order to preserve substantially intact their business
      organization.

    Abacus has also agreed that, until the completion of the merger or unless
DoubleClick consents in writing, Abacus and its subsidiaries will conduct their
business in compliance with the following specific restrictions:

    - the modification of Abacus's certificate of incorporation or bylaws;

    - the issuance, sale, pledge or encumbrance of shares of Abacus capital
      stock or securities convertible into Abacus capital stock, except for
      limited issuances of securities in connection with stock options already
      outstanding or the exercise of outstanding stock options under Abacus's
      stock option plans;

    - the disposition of any properties or assets other than entering into
      alliance agreements or providing products and services in the ordinary
      course of business consistent with past practice;

    - the acquisition of interests in other entities;

    - the incurrence of any material indebtedness;

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    - the assumption of any material indebtedness of any person other than a
      subsidiary;

    - the making of any material loan or advance, other than routine loans under
      a specified amount to employees who are not executive officers;

    - the entrance into or modification or termination of material contracts;

    - the making of capital expenditures, other than those that have been made
      in the ordinary course, that have been budgeted for fiscal year 1999 and
      disclosed to DoubleClick and that do not exceed in the aggregate a
      specified amount for Abacus and its subsidiaries;

    - the declaration, setting aside or issuance of dividends or other
      distributions, except by Abacus's subsidiaries to Abacus or other
      subsidiaries;

    - any reclassification or other modification of any of its capital stock;

    - the modification of any stock options or authorization of cash payments in
      exchange for stock options;

    - the amendment, repurchase, or redemption of any securities by Abacus's
      subsidiaries;

    - the increase of compensation payable to directors, officers, consultants
      or employees;

    - the granting of any severance arrangements or entering into of any
      agreement providing benefits upon a change of control that would be
      triggered by the merger;

    - the adoption, entering into or amendment of any plan, agreement, policy or
      arrangement for the benefit of any director, officer, consultant or
      employee except to the extent required by applicable law or an existing
      collective-bargaining agreement;

    - the entering into or amendment of any contract, commitment or arrangement
      with any of Abacus's directors, officers, consultants or employees;

    - the payment of indebtedness other than in the ordinary course consistent
      with past practice or reserved against on Abacus's consolidated balance
      sheet;

    - modifications to accounting policies and procedures;

    - the making of material tax elections, settlements or compromises; and

    - authorizing or taking any action that would make untrue any of the
      representations or warranties of Abacus in the merger agreement.

    Abacus has also agreed to provide tax information to DoubleClick, and
DoubleClick has agreed not to take any action that would have a principal
purpose of and would reasonably be likely to result in delaying or interfering
with the consummation of the merger. Each of Abacus and DoubleClick has also
agreed:

    - to notify the other promptly of material events affecting the merger or
      the parties' rights under the merger agreement;

    - to provide reasonable access to the other to its facilities and records;

    - to use its reasonable efforts to cause the merger to qualify as a
      reorganization and to be treated as a pooling of interests;

    - to make all necessary filings and obtain any consents and approvals as may
      be required in connection with the merger agreement and the merger; and

    - to provide the other copies of its filings with the Securities Exchange
      Commission.

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    The agreements related to the conduct of Abacus's business in the merger
agreement are complicated and not easily summarized. We urge stockholders to
carefully read the article in the merger agreement entitled "Conduct Prior to
the Effective Time."

NO SOLICITATION OF TRANSACTIONS

    Until the merger agreement is terminated or as otherwise provided in the
merger agreement, Abacus has agreed not to take any of the following actions,
directly or indirectly:

    - solicit, initiate, encourage or agree to any takeover proposal or other
      extraordinary transaction by a third party; or

    - negotiate with, or disclose any nonpublic information relating to Abacus
      or any of its subsidiaries to, or allow access to any of their properties,
      books or records to, any person that has advised Abacus that it may
      consider making, or that has made, a takeover or extraordinary transaction
      proposal.

    An "extraordinary transaction" includes:

    - a merger, consolidation or similar transaction;

    - a proposal to acquire 20% or more of its outstanding capital stock or
      assets; or

    - a license, joint venture or other arrangement in which Abacus provides or
      permits access to its data to a third party, if a primary purpose of the
      third party is targeted Internet, Web, e-mail or interactive television
      advertising.

    The Abacus board is not prohibited, however, from taking and disclosing to
Abacus's stockholders a position with respect to a tender or exchange offer
under Rules 14d-9 and 14e-2(a) under the Exchange Act not made in violation of
the merger agreement.

    Abacus has agreed to provide DoubleClick prompt notice and detailed
information of any extraordinary transaction proposal it receives. Abacus may,
however, engage in any of the foregoing actions, other than solicitation,
initiation or encouragement of any extraordinary transaction proposal, if:

    - the Abacus board concludes in good faith after advice from outside legal
      counsel that this action is necessary to prevent the board from violating
      its fiduciary duties under applicable law;

    - any cash consideration is involved, and this consideration is not subject
      to a financing contingency, and the board determines based upon advice of
      its independent financial advisors in the exercise of its fiduciary duties
      that the acquiring party is capable of consummating the competing
      extraordinary transaction as proposed; and

    - the Abacus board has determined in the exercise of its fiduciary duties
      that the competing extraordinary transaction provides greater value (based
      on a written opinion from its financial advisors) to Abacus stockholders
      than the merger.

DIRECTOR AND OFFICER INDEMNIFICATION AND INSURANCE

    The merger agreement provides that, after the completion of the merger, all
rights of indemnification, advancement of expenses, exculpation, limitation of
liability and similar rights existing in favor of present and former officers,
directors, employees and agents of Abacus shall survive the merger and shall
continue for six years from the effective time. The merger agreement also
provides that, for six years after the completion of the merger, DoubleClick
will either:

    - maintain the directors' and officers' liability insurance currently
      maintained by Abacus; or

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    - if not available, maintain directors' and officers' liability insurance
      with coverage and terms substantially as favorable to the directors and
      officers as the Abacus directors' and officers' liability insurance policy
      in effect on the date of the merger agreement.

    DoubleClick is not required to pay premiums in excess of 150% of the annual
amount Abacus currently paid for this insurance.

CONDITIONS TO THE MERGER

    DoubleClick's and Abacus's obligations to complete the merger and the
related transactions are subject to the satisfaction or waiver of each of the
following conditions before completion of the merger:

    - the registration statement relating to the issuance of shares of
      DoubleClick common stock as contemplated by the merger agreement must be
      declared effective by the SEC;

    - the merger agreement must be approved by a majority of the outstanding
      shares of Abacus common stock and the DoubleClick share issuance must be
      approved by DoubleClick's stockholders;

    - no order, writ, injunction or decree exists that makes the merger illegal
      or otherwise prohibits completion of the merger;

    - any waiting period under the antitrust laws that applies to the
      consummation of the merger must have expired or been terminated;

    - all consents, approvals and authorization legally required to consummate
      the merger must have been obtained from all governmental entities, except
      where no material adverse effect could reasonably be expected to occur;
      and

    - the shares of DoubleClick common stock to be issued in connection with the
      merger must be approved for listing with the Nasdaq National Market.

    Abacus's obligations to complete the merger and the other transactions
contemplated by the merger agreement are subject to the satisfaction or waiver
of each of the following additional conditions before completion of the merger:

    - DoubleClick's representations and warranties must be true and correct when
      made and as of the closing of the merger, except where failures to be true
      and correct would not have a material adverse effect on DoubleClick;

    - DoubleClick must have complied in all material respects with all of its
      covenants in the merger agreement; and

    - Abacus must have received the opinion of its counsel, Kane Kessler, P.C.,
      or another law firm or professional services firm acceptable to
      DoubleClick, to the effect that the merger will constitute a
      reorganization within the meaning of Section 368(a) of the Internal
      Revenue Code.

    DoubleClick's obligations to complete the merger and the other transactions
contemplated by the merger agreement are subject to the satisfaction or waiver
of each of the following additional conditions before completion of the merger:

    - Abacus's representations and warranties must be true and correct when made
      and as of the closing of the merger, except where failures to be true and
      correct would not have a material adverse effect on Abacus;

    - Abacus must have complied in all material respects with all of its
      covenants in the merger agreement;

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    - DoubleClick must have received the opinion of its tax counsel, Brobeck,
      Phleger & Harrison LLP, to the effect that the merger will constitute a
      reorganization within the meaning of Section 368(a) of the Internal
      Revenue Code;

    - DoubleClick must be advised in writing by PricewaterhouseCoopers LLP
      regarding the concurrence with DoubleClick's management as to the
      appropriateness of pooling-of-interests accounting for the merger in
      accordance with U.S. generally accepted accounting procedures and the
      accounting standards of the Securities Exchange Commission;

    - Abacus must be advised in writing by PricewaterhouseCoopers LLP regarding
      their concurrence with Abacus's management that no conditions exist that
      would preclude Abacus from being a party to a business combination
      accounted for as a pooling of interests;

    - no change in or effect on the business of Abacus and its subsidiaries
      exists that, individually or in the aggregate, is or is reasonably likely
      to be materially adverse to the business, assets, liabilities, financial
      condition or results of operations of Abacus and its subsidiaries, taken
      as a whole;

    - all third-party consents required under any material contract of Abacus as
      a result of the merger must be obtained; and

    - the following employees of Abacus must accept employment with DoubleClick
      and must enter into employment and non-competition agreements
      substantially in the forms attached to the merger agreement: M. Anthony
      White, Daniel C. Snyder, Carlos E. Sala, Christopher M. Dice and Brian M.
      Rainey.

TERMINATION OF THE MERGER AGREEMENT

    The merger agreement may be terminated at any time before the completion of
the merger, as summarized below:

    - the merger agreement may be terminated by our mutual consent; or

    - the merger agreement may also be terminated by either of us if the
      conditions to completion of the merger would not be satisfied because of
      either (A) a breach of an agreement in the merger agreement by the other
      party or (B) a breach of a representation or warranty of the other party
      in the merger agreement, and the breaching party does not take reasonable
      steps to cure the breach.

    In addition, the merger agreement may be terminated by either of us under
any of the following circumstances:

    - if the merger is not completed, without the fault of the terminating
      party, by December 31, 1999;

    - if a final court or governmental order prohibiting the merger is issued
      and is not appealable;

    - if the DoubleClick stockholders do not approve the issuance of DoubleClick
      common stock at the DoubleClick special meeting; or

    - if the Abacus stockholders do not approve the merger agreement and the
      merger at the Abacus special meeting.

    Furthermore, the merger agreement may be terminated by DoubleClick if any of
the following occur:

    - Abacus's board withdraws or modifies in a manner adverse to DoubleClick
      its recommendation as to the merger agreement or the merger, or resolves
      to do so;

    - Abacus fails to comply with the nonsolicitation provisions contained in
      the merger agreement, which are discussed in more detail in "--No
      Solicitation of Transactions" on page 64; or

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    - with respect to an extraordinary transaction as described in more detail
      in "--No Solicitation of Transactions" on page 64, Abacus's board
      recommends one of these transactions to its stockholders, fails to
      recommend against its acceptance by its stockholders, fails to reconfirm
      its approval and recommendation of the merger with DoubleClick or
      determines that this extraordinary transaction is superior and takes
      permitted actions in furtherance of negotiating the transaction, or
      resolves to do any of these.

PAYMENT OF FEES AND EXPENSES

    Whether or not the merger is consummated, all costs and expenses incurred in
connection with the merger agreement and the merger will be paid by the party
incurring the expense, except that expenses incurred in connection with
printing, filing and mailing the joint proxy statement/prospectus and the
registration statement, other than attorney's and accountant's fees and
expenses, shall be shared equally.

    Abacus has agreed to pay DoubleClick a cash termination fee of
$30.0 million in addition to reimbursing DoubleClick for its out-of-pocket
expenses up to $2.5 million in the following circumstances:

    - DoubleClick terminates the merger agreement as a result of Abacus board's
      withdrawing, modifying or changing its recommendation in favor of the
      merger in a manner adverse to DoubleClick, unless prior to the termination
      there was no existing or proposed competing extraordinary transaction and
      Abacus's financial advisor had withdrawn its fairness opinion;

    - DoubleClick terminates the merger agreement as a result of Abacus's
      board's recommendation of a competing extraordinary transaction;

    - DoubleClick terminates the merger agreement as a result of Abacus's
      failure to comply in all material respects with the prohibitions on
      solicitations of transactions, as more fully described in "--No
      Solicitation of Transactions" on page 64;

    - DoubleClick terminates the merger agreement as a result of a competing
      extraordinary transaction's being publicly announced or otherwise publicly
      known and the Abacus board either:

     - fails to recommend against the competing extraordinary transaction;

     - fails to reconfirm its approval and recommendation of the merger
       agreement and the transactions contemplated by the merger agreement
       within five days of DoubleClick's written request to do so; or

     - determines that the competing extraordinary transaction is a superior
       proposal and provides information in connection with or negotiates the
       competing extraordinary transaction;

    - DoubleClick terminates the merger agreement as a result of Abacus's
      board's resolving to take any of the actions described above;

    - DoubleClick or Abacus terminates the merger agreement as a result of the
      effective time not occurring on or before December 31, 1999 and (A) at or
      prior to the termination, a competing extraordinary transaction existed
      and (B) within 12 months after the termination, Abacus enters into a
      definitive agreement with respect to a competing extraordinary transaction
      or consummates any competing extraordinary transaction; and

    - DoubleClick or Abacus terminates the merger agreement as a result of the
      merger agreement and the merger not receiving the requisite votes for
      approval by Abacus's stockholders and (A) at or prior to the termination,
      a competing extraordinary transaction existed and (B) within 12 months
      after the termination, Abacus enters into a definitive agreement with
      respect to a competing extraordinary transaction or consummates any
      competing extraordinary transaction.

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    If DoubleClick terminates the merger agreement as a result of Abacus's
board's withdrawing, modifying or changing its recommendation in favor of the
merger in a manner adverse to DoubleClick, and prior to this termination, no
competing extraordinary transaction had existed or been proposed and Abacus's
financial advisor had withdrawn its fairness opinion, Abacus may pay up to
$25.0 million of the termination fee with its shares of common stock valued at
$93.25 per share and pay the remainder of the termination fee in cash.

    If DoubleClick terminates the merger agreement

    - because the effective time did not occur on or before December 31, 1999;

    - because of the failure to obtain the requisite approval by Abacus's
      stockholders; or

    - because of a breach of any representation, warranty, covenant or
      agreement;

and there is an impending competing extraordinary transaction involving a
license, joint venture or other arrangement where Abacus provides or permits
access to its data to a third party, and a primary purpose of the party is
targeted Internet, Web, e-mail or interactive television advertising, Abacus
could either pay the $30.0 million termination fee, or, at its election
(A) offer DoubleClick a right of first refusal to this license or other
arrangement or (B) offer DoubleClick the opportunity to enter into this license
or other arrangement on the same terms as the third party.

    Abacus would be required to pay DoubleClick's out-of-pocket expenses up to
$2.5 million if DoubleClick terminates the merger agreement as a result of
Abacus's breach of any representation, warranty, covenant or agreement in the
merger agreement or as a result of any of Abacus's representations or warranties
becoming untrue, incomplete or incorrect, where Abacus would thereby fail to
meet its closing obligations, unless the condition is curable within 20 days and
Abacus applies reasonable efforts to cure the condition. If Abacus subsequently
enters into a definitive agreement with respect to any competing extraordinary
transaction or consummates any competing extraordinary transaction within
12 months of the termination, Abacus must also pay DoubleClick the
$30.0 million termination fee.

    DoubleClick would be required to pay Abacus's out-of-pocket expenses up to
$2.5 million if Abacus terminates the merger agreement as a result of
DoubleClick's breach of any representation, warranty, covenant or agreement in
the merger agreement or as a result of any of DoubleClick's representations or
warranties becoming untrue, incomplete or incorrect, where DoubleClick would
thereby fail to meet its closing obligations, unless the condition is curable
within 20 days and DoubleClick applies reasonable efforts to cure the condition.

EXTENSION, WAIVER AND AMENDMENT OF THE MERGER AGREEMENT

    DoubleClick and Abacus may amend the merger agreement before completion of
the merger; provided, however, after the Abacus stockholders adopt the merger
agreement, no change may be made to the amount or type of consideration into
which Abacus common stock will be converted.

    Either DoubleClick or Abacus may, in writing, extend the other's time for
the performance of any of the obligations or other acts under the merger
agreement, waive any inaccuracies in the other's representations and warranties
and waive compliance by the other with any of the agreements or conditions
contained in the merger agreement.

RELATED AGREEMENTS

    STOCK OPTION AGREEMENT

    DoubleClick required Abacus to enter into a stock option agreement as a
prerequisite to entering into the merger agreement. DoubleClick did not pay any
monetary consideration in exchange for the stock option agreement. A copy of the
stock option agreement is attached as APPENDIX B to this joint proxy

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statement/prospectus and is incorporated by reference in this joint proxy
statement/prospectus. The stock option agreement grants DoubleClick the
irrevocable option to purchase up to 1,974,516 shares of Abacus common stock, at
an exercise price of $93.25 per share, not to exceed 19.99% of Abacus's
outstanding common stock. DoubleClick may exercise the option, in whole or in
part, at any time (A) after the termination of the merger agreement in any of
the circumstances that entitle DoubleClick to the payment of the $30.0 million
termination fee and the reimbursement of expenses up to $2.5 million, and
(B) before Abacus enters into a definitive agreement with respect to a competing
extraordinary transaction or consummates any other competing extraordinary
transaction, following the termination of the merger agreement as a result of:

    - a breach of any representation, warranty or covenant by Abacus;

    - the effective time of the merger not occurring on or before December 31,
      1999; or

    - the merger agreement and the merger not receiving the requisite votes for
      approval by Abacus's stockholders.

    DoubleClick is restricted under the agreement to profits not exceeding
$50 million (including the termination fee payable under the merger agreement)
in the aggregate. In the event its profits would exceed this amount, DoubleClick
in its sole discretion shall either:

    - reduce the number of shares of Abacus common stock to be subject to the
      option;

    - pay cash to Abacus;

    - receive a smaller termination fee;

    - deliver to Abacus for cancellation Abacus shares that DoubleClick
      previously purchased; or

    - take any combination of the above actions in order to limit its profits to
      $50 million in the aggregate.

    DoubleClick is entitled to receive for each share of Abacus common stock
with respect to which an option has not been exercised an amount equal to
(A) the per-share amount of consideration to be received by a holder of one
share of Abacus common stock, less (B) the exercise price of $93.25, if Abacus
enters into an agreement:

    - to consolidate with or merge into any person other than DoubleClick or its
      subsidiary, where Abacus would not be the surviving company;

    - to permit any person other than DoubleClick or its subsidiary to merge
      into Abacus, where Abacus is the surviving corporation and its
      then-outstanding common stock is changed into or exchanged for securities
      of another person, cash or other property or its outstanding common stock
      immediately prior to the merger represents less than 50% of the
      outstanding stock of the merged company; or

    - to sell or otherwise transfer or sell all or substantially all of its
      assets to any person other than DoubleClick or its subsidiaries.

    At any time while the option is exercisable, upon demand, DoubleClick has
the right to sell to Abacus, and Abacus must purchase from DoubleClick, all or
any portion of shares of Abacus common stock acquired through DoubleClick's
option. The purchase price for each share is the difference between (A) the
market or tender offer price as of the date of DoubleClick's notice to Abacus
and (B) the exercise price of $93.25.

    Following any exercise of its option, DoubleClick may by written notice to
Abacus request that Abacus register under the Securities Act all or any part of
DoubleClick's shares acquired under the stock option agreement, where the shares
equal at least 4% of Abacus's outstanding common stock. DoubleClick's

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notice must include a certificate executed by DoubleClick and its proposed
managing underwriter stating that the manager in good faith believes that, based
on then-prevailing market conditions, it will be able to sell the shares at a
per share price equal to at least 70% of their fair market value. DoubleClick is
entitled to two of these registrations. Any right to require registration will
terminate with respect to any shares that may be sold in any 90-day period under
Rule 144 of the Securities Act.

    The option is intended to increase the likelihood that the merger will be
completed. Consequently, aspects of the stock option agreement may have the
effect of discouraging persons who might now or at any time prior to the merger
be interested in acquiring all or a significant interest in Abacus or its assets
before completion of the merger.

    STOCKHOLDER AGREEMENTS

    In connection with the merger, each of M. Anthony White, Daniel C. Snyder,
Antony Lee, Robert L. North, Frank Kenny, Christopher M. Dice and Carlos E. Sala
have entered into a stockholder agreement with DoubleClick. A copy of a form of
the stockholder agreement is attached as APPENDIX C to this joint proxy
statement/prospectus and is incorporated by reference in this joint proxy
statement/prospectus. The terms of the stockholder agreement provide that the
stockholders will vote all shares of Abacus common stock beneficially owned by
them, or any new shares of Abacus stock they may acquire, in favor of the
approval of the merger agreement and the merger. In connection with the
stockholder agreements, each of the stockholders has executed an irrevocable
proxy to vote their shares in favor of the approval of the merger agreement and
the merger. As of August 31, 1999, the Abacus stockholders who entered into the
stockholder agreement collectively held approximately 505,500 shares of Abacus
common stock which represented approximately 5% of the outstanding Abacus common
stock. None of the stockholders who are parties to the stockholder agreement was
paid additional consideration in connection with the stockholder agreement.

    EMPLOYMENT AGREEMENTS

    Concurrently with the effectiveness of the merger, DoubleClick and Abacus
plan to enter into employment agreements with M. Anthony White, Daniel C.
Snyder, Carlos E. Sala, Christopher M. Dice and Brian M. Rainey. Under the terms
of the proposed employment agreements, each employee agrees to remain with
Abacus for a period of one year from the closing of the merger unless Abacus
terminates them or they resign earlier.

    If the employee's employment is terminated other than in connection with a
"change in control" (A) by Abacus without "Cause," (B) by the employee upon a
material breach by Abacus of its obligations under the employment agreement, if
the breach continues for 30 days after receipt of written notice from the
employee, or (C) at the expiration of the employment agreement due to
nonrenewal, then the employee will be entitled to receive a severance payment
equaling 12 months of his base salary then in effect and incentive compensation,
if earned, on a pro-rated basis. If the employment is terminated for Cause prior
to the end of the 12-month period, then the employee will be paid all salary,
bonus and benefits earned through the date of termination of employment, but
nothing else.

    If the employee's employment is terminated by the employee or by Abacus upon
or within four months following a change in control, the employee will be
entitled to receive (A) his full base salary and bonus through the date of
termination at the rate applicable at the time the notice of termination is
given, and (B) a severance payment equal to 24 months of his base salary then in
effect plus two times any incentive and bonus compensation earned in the last
complete fiscal year. In Brian Rainey's case, the applicable severance payment
equals 12 months of his base salary then in effect.

    "Cause" shall mean the employee's termination as a result of: (A) a breach
by the employee of any material provision in the employment agreement; (B) the
employee's gross negligence or willful misconduct in connection with the
performance of his duties under the employment agreement; (C) the

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employee's misappropriation for personal use of the assets or business
opportunities of Abacus; (D) the employee's embezzlement of Abacus's funds or
property; (E) fraud on the employee's part; or (F) the employee's conviction in
any felony.

    A "change in control" shall mean that any person is or becomes the
beneficial owner of securities representing 40% or more of the combined voting
power of Abacus's then-outstanding securities. The merger will be considered a
change in control only if DoubleClick breaches its obligations under the
employment agreement to provide stock options to the employee under its 1997
Stock Incentive Plan on terms and at a level reasonable in light of the
employee's responsibilities and comparably to existing arrangements with peer
employees at DoubleClick and Abacus.

    NON-COMPETITION AND NON-DISCLOSURE AGREEMENTS

    Concurrently with the execution of employment agreements, M. Anthony White,
David C. Snyder, Carlos E. Sala, Christopher M. Dice and Brian M. Rainey will be
required to execute non-competition and non-disclosure agreements with Abacus.
The non-competition and non-disclosure agreements require the employee, during
his employment and for a one-year period following his termination:

    - not to engage, individually or on behalf of other persons, in any business
      for, or consult or assist any business or legal entity that competes with
      Abacus or any affiliate, including DoubleClick;

    - unless waived in writing by Abacus, not to solicit any customers or known
      prospective customers of Abacus or any affiliate, including DoubleClick,
      to the extent that the solicitation would relate to Abacus's or any
      affiliate's, including DoubleClick's, confidential information or
      business; and

    - not to engage, individually or on behalf of other persons, in soliciting
      any employees or consultants of Abacus to leave their employment with
      Abacus or any affiliate, including DoubleClick, in order to accept a
      position of any kind with another employer.

    In addition, each non-competition and non-disclosure agreement prohibits the
employee from divulging or disclosing any confidential information of Abacus
without the written consent of DoubleClick's chief executive officer.

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       PROPOSAL TO APPROVE DOUBLECLICK INC. EMPLOYEE STOCK PURCHASE PLAN

    DoubleClick's stockholders are also being asked to approve the DoubleClick
Inc. Employee Stock Purchase Plan, under which 500,000 shares of common stock
will initially be reserved for issuance. (Abacus stockholders are not being
asked, and are not entitled, to approve or disapprove of the DoubleClick
purchase plan.)

    The DoubleClick purchase plan is intended to provide eligible employees of
DoubleClick and its participating affiliates with the opportunity to acquire a
proprietary interest in DoubleClick through a payroll-deduction based employee
stock purchase plan designed to operate in compliance with Section 423 of the
Internal Revenue Code. The DoubleClick purchase plan is expected to be adopted
by DoubleClick's Board of Directors by its meeting scheduled for October 28,
1999 and will become effective on February 1, 2000 if approved by DoubleClick's
board of directors and by the stockholders at DoubleClick's special meeting.

    In connection with DoubleClick's acquisition of NetGravity, DoubleClick
assumed NetGravity's 1998 Employee Stock Purchase Plan. Pursuant to this
assumption, the employees of NetGravity who had enrolled in the NetGravity
purchase plan prior to the acquisition (approximately 101 employees) will be
entitled to purchase shares of DoubleClick common stock on January 31, 2000 and
July 31, 2000. Based on the current fair market value of the common stock, a
maximum of 27,855 shares of common stock will be issued under the NetGravity
purchase plan through July 31, 2000.

    The following is a summary of the principal features of the DoubleClick
purchase plan. Except as noted below, the principal features of the NetGravity
purchase plan are substantially the same as those features summarized below for
the DoubleClick purchase plan. The summary, however, does not purport to be a
complete description of all the provisions of the DoubleClick purchase plan. Any
stockholder of DoubleClick who wishes to obtain a copy of the actual plan
document may do so upon written request to DoubleClick's Secretary at
DoubleClick's principal executive offices in New York, New York.

SHARE RESERVE

    DoubleClick has initially reserved 500,000 shares of common stock for
issuance over the ten-year term of the DoubleClick purchase plan. This initial
share reserve is in addition to the shares of common stock that will be issued
under the NetGravity purchase plan. The share reserve will automatically
increase on the first trading day of each calendar year beginning in the year
2001 by 1% of the total number of shares of common stock outstanding on the last
trading day in December of the immediately preceding calendar year. In no event,
however, will any such annual increase exceed 450,000 shares.

    In the event any change is made to the outstanding shares of common stock by
reason of any recapitalization, stock dividend, stock split, combination of
shares, exchange of shares or other change in corporate structure effected
without DoubleClick's receipt of consideration, appropriate adjustments will be
made to

    -  the maximum number and class of securities issuable under the DoubleClick
      purchase plan,

    -  the maximum number and class of securities by which the share reserve may
      increase each year,

    -  the maximum number and class of securities purchasable per participant on
      any one purchase date and

    -  the class and maximum number of securities subject to each outstanding
      purchase right and the purchase price payable per share thereunder.

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ADMINISTRATION

    The DoubleClick purchase plan will be administered by the Compensation
Committee of DoubleClick's board. This committee, as Plan Administrator, will
have full authority to adopt rules and procedures as it may deem necessary for
proper plan administration and to interpret the provisions of the DoubleClick
purchase plan. All costs and expenses incurred in plan administration will be
paid by DoubleClick without charge to participants.

OFFERING PERIODS

    Under the DoubleClick purchase plan, shares will be issued through a series
of successive offering periods, each of a duration of up to 24 months. The
length of each offering period and the purchase periods in each offering period
will be determined by the Plan Administrator. Each participant will be granted a
separate right to purchase shares of common stock for each offering period in
which he or she participates. The purchase right will be granted on the first
business day of each purchase period and will be automatically exercised on the
last business day of each purchase period. Each purchase right entitles the
participant to purchase the whole number of shares of Common Stock obtained by
dividing the participant's payroll deductions for the purchase period by the
purchase price in effect for such period. If the fair market value per share of
DoubleClick common stock on any purchase date is less than the fair market value
per share on the start date of the two-year offering period, then that offering
period will automatically terminate, and a new two-year offering period will
begin on the next business day. All participants in the terminated offering will
be transferred to the new offering period. The NetGravity purchase plan contains
consecutive, overlapping 24-month offering periods, each of which contains four
six-month purchase periods.

ELIGIBILITY

    Any individual who customarily works for more than 20 hours per week and for
more than five months per calendar year in the employ of DoubleClick or any
participating affiliate will be eligible to participate in the purchase plan. An
individual who is an eligible employee at the start of any offering period may
join that period at that time or at any later entry date. Individuals who become
eligible employees after the start date of an offering period may join the
DoubleClick purchase plan on any subsequent entry date, as specified by the Plan
Administrator within that offering period.

    Participating affiliates include any parent or subsidiary corporations of
DoubleClick, whether now existing or hereafter organized, which elect, with the
approval of the Plan Administrator, to extend the benefits of the purchase plan
to their eligible employees.

    As of October 19, 1999, approximately 101 employees, including executive
officers, would be eligible to participate in the DoubleClick purchase plan.

PAYROLL DEDUCTIONS

    The purchase price will be paid through payroll deductions determined as a
percentage of base salary or total cash compensation as determined by the Plan
Administrator. Each participant may authorize payroll deductions in any multiple
of 1% up to a maximum of 10% of his or her base salary or total compensation.
The NetGravity purchase plan permits deductions of up to 10% of a participant's
compensation.

PURCHASE PRICE

    The purchase price per share at which common stock will be purchased on the
participant's behalf on each purchase date will be equal to 85% of the lower of
(A) the fair market value per share of common

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stock on the start date of the purchase period during which the participant
joins the offering period or (B) the fair market value per share of common stock
on that purchase date.

PURCHASE PROVISIONS

    On the last business day of each purchase period, the accumulated payroll
deductions of each participant will automatically be applied to the purchase of
whole shares of common stock at the purchase price in effect for the participant
for that purchase period. However, no participant may purchase more than
250 shares of common stock per purchase period, subject to periodic adjustments
in the event of specified changes in DoubleClick's capitalization. The maximum
aggregate number of shares of DoubleClick common stock purchasable by all
participants on any one purchase date shall not exceed 125,000 shares, subject
to periodic adjustments in the event of specified changes in DoubleClick's
capitalization. The Plan Administrator shall have discretionary authority,
exercisable prior to the start of any offering period under the DoubleClick
purchase plan, to increase or decrease the limitations to be in effect for the
number of shares purchasable per participant and in the aggregate by all
participants on each purchase date during that offering period. The NetGravity
purchase plan allows for a maximum of 5,000 shares to be purchased by a
participant during a single purchase period.

VALUATION

    The fair market value per share of DoubleClick common stock on any relevant
date will be the closing selling price per share on that date on the Nasdaq
National Market. On October 19, 1999, the fair market value per share of
DoubleClick common stock was $119.06 per share.

SPECIAL LIMITATIONS

    The DoubleClick purchase plan imposes limitations upon a participant's
rights to acquire common stock, including the following limitations:

    -  No purchase right may be granted to any individual who owns stock
       (including stock purchasable under any outstanding purchase rights)
       equalling 5% or more of the total combined voting power or value of all
       classes of stock of DoubleClick of any of its affiliates.

    -  No purchase right granted to a participant may permit the individual to
       purchase common stock at a rate greater than $25,000 worth of common
       stock (valued at the time such purchase right is granted) for each
       calendar year the purchase right remains outstanding at any time.

    -  No participant may purchase more than 250 shares of common stock on any
       one purchase date.

TERMINATION OF PURCHASE RIGHTS

    The purchase right will immediately terminate upon the participant's loss of
eligible employee status or upon his or her affirmative withdrawal from the
purchase period. The payroll deductions collected for the purchase period in
which the participant withdraws may, at the participant's election, be
immediately refunded or applied to the purchase of common stock at the end of
that purchase period. The payroll deductions collected for the purchase period
in which the participant ceases to be an eligible employee will be immediately
refunded.

STOCKHOLDER RIGHTS

    No participant will have any stockholder rights with respect to the shares
of common stock covered by his or her purchase right until the shares are
actually purchased on the participant's behalf. No adjustment will be made for
dividends, distributions or other rights for which the record date is prior to
the date of such purchase.

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ASSIGNABILITY

    No purchase right will be assignable or transferable other than in
connection with the participant's death and will be exercisable only by the
participant during his or her lifetime.

CHANGE IN CONTROL

    If there is a change in control of DoubleClick, whether by merger, asset
sale or sale of stock by the stockholders during a purchase period, all
outstanding purchase rights will automatically be exercised immediately prior to
the effective date of the transaction. The purchase price will be 85% of the
lower of

    -  the fair market value per share of common stock on the entry date of the
       offering period during which the change in control occurs, or

    -  the fair market value per share of common stock immediately prior to the
       transaction.

AMENDMENT AND TERMINATION

    The purchase plan will terminate upon the earliest to occur of

    -  the first business day of January 2010,

    -  the date on which all available shares are issued, or

    -  the date on which all outstanding purchase rights are exercised in
       connection with a change in control of DoubleClick.

    The DoubleClick board of directors may at any time alter, suspend or
discontinue the DoubleClick purchase plan. However, the board of directors may
not, without stockholder approval,

    -  materially increase the number of shares issuable under the DoubleClick
       purchase plan or the maximum aggregate number of purchasable shares on
       any one purchase date except in connection with certain changes in
       DoubleClick's capital structure,

    -  alter the purchase price formula so as to reduce the purchase price, or

    -  materially modify the requirements for eligibility to participate in the
       DoubleClick purchase plan.

PLAN BENEFITS

    No purchase rights have been granted and no shares have been purchased under
the DoubleClick purchase plan.

FEDERAL TAX CONSEQUENCES

    The DoubleClick purchase plan is intended to be an "employee stock purchase
plan" within the meaning of Section 423 of the Internal Revenue Code. Under a
plan which so qualifies, no taxable income will be recognized by a participant,
and no deductions will be allowable to DoubleClick, in connection with the grant
or the exercise of an outstanding purchase right. Taxable income will not be
recognized until there is a sale or other disposition of the shares acquired
under the DoubleClick purchase plan or in the event the participant should die
while still owning the purchased shares.

    If the participant sells or otherwise disposes of the purchased shares
within two years after the start date of the purchase period in which the shares
were acquired and within one year after the actual purchase date of such shares,
then (A) the participant will recognize ordinary income in the year of sale or
disposition equal to the amount by which the fair market value of the shares on
the purchase date exceeded the purchase price paid for those shares, and (B)
DoubleClick will be entitled to an income tax deduction, for the taxable year in
which the sale or disposition occurs, equal in amount to such excess.

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    If the participant sells or disposes of the purchased shares more than two
years after the start date of the purchase period in which the shares were
acquired and after one year after the actual purchase date of such shares, then
the participant will recognize ordinary income in the year of sale or
disposition equal to the lesser of (A) the amount by which the fair market value
of the shares on the sale or disposition date exceeded the purchase price paid
for those shares or (B) 15% of the fair market value of the shares on the start
date of that purchase period, and any additional gain upon the disposition will
be taxed as a long-term capital gain. DoubleClick will not be entitled to any
income tax deduction with respect to such sale or disposition.

    If the participant still owns the purchased shares at the time of death, the
lesser of (A) the amount by which the fair market value of the shares on the
date of death exceeds the purchase price or (B) 15% of the fair market value of
the shares on the start date of the purchase period in which those shares were
acquired will constitute ordinary income in the year of death.

ACCOUNTING TREATMENT

    Under current accounting rules, the issuance of common stock under the
DoubleClick purchase plan will not result in a compensation expense chargeable
against DoubleClick's reported earnings. However, DoubleClick must disclose, in
pro forma statements to DoubleClick's financial statements, the impact the
purchase rights granted under the purchase plan would have upon DoubleClick's
reported earnings if the value of those purchase rights were treated as
compensation expense.

STOCKHOLDER APPROVAL

    The affirmative vote of a majority of the outstanding voting shares of
DoubleClick present or represented and entitled to vote at the DoubleClick
special meeting is required for approval of the DoubleClick purchase plan.
Should stockholder approval not be obtained, then the DoubleClick purchase plan
will not be implemented, and no purchase rights will be granted and no stock
issuances will be made under the DoubleClick purchase plan.

    THE DOUBLECLICK BOARD OF DIRECTORS ANTICIPATES ADOPTING THE DOUBLECLICK
PURCHASE PLAN BY ITS MEETING SCHEDULED FOR OCTOBER 28, 1999 AND RECOMMENDS THAT
THE STOCKHOLDERS VOTE FOR THE APPROVAL OF THE DOUBLECLICK PURCHASE PLAN. THE
BOARD BELIEVES THAT IT IS IN THE BEST INTERESTS OF DOUBLECLICK TO IMPLEMENT A
PROGRAM OF STOCK OWNERSHIP FOR DOUBLECLICK'S EMPLOYEES IN ORDER TO PROVIDE THEM
WITH A MEANINGFUL OPPORTUNITY TO ACQUIRE A SUBSTANTIAL PROPRIETARY INTEREST IN
DOUBLECLICK AND THEREBY ENCOURAGE THEM TO REMAIN IN DOUBLECLICK'S SERVICE AND
MORE CLOSELY ALIGN THEIR INTERESTS WITH THOSE OF THE STOCKHOLDERS.

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          UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS

    On June 13, 1999, DoubleClick entered into an agreement to merge with Abacus
in a transaction expected to be accounted for as a pooling of interests. Under
the terms of the agreement, each issued and outstanding share of Abacus common
stock will be exchanged for 1.05 shares of DoubleClick common stock.
Additionally, DoubleClick will convert approximately 1.4 million Abacus stock
options into approximately 1.5 million DoubleClick stock options.

    On July 12, 1999, DoubleClick entered into an agreement to merge with
NetGravity in a transaction expected to be accounted for as a pooling of
interests. Under the terms of the agreement, each issued and outstanding share
of NetGravity common stock will be exchanged for 0.28 shares of DoubleClick
common stock. Additionally, DoubleClick will convert approximately 3.3 million
NetGravity stock options into approximately 924,000 DoubleClick stock options.

    The following unaudited pro forma condensed combined financial statements
present the effect of the proposed mergers between DoubleClick and Abacus and
between DoubleClick, Abacus and NetGravity expected to be accounted for as
poolings of interests. The unaudited pro forma condensed combined balance sheet
presents the combined financial position of DoubleClick and Abacus and of
DoubleClick, Abacus and NetGravity as of June 30, 1999 assuming that the
proposed mergers had occurred as of June 30, 1999. This pro forma information is
based upon the historical consolidated balance sheet data of DoubleClick and
Abacus and the historical consolidated balance sheet data of NetGravity as of
that date. The unaudited pro forma condensed combined statements of operations
give effect to the proposed mergers of DoubleClick and Abacus and of
DoubleClick, Abacus and NetGravity by combining the results of operations of
DoubleClick for the six months ended June 30, 1999 and 1998, for each of the two
years in the period ended December 31, 1998, and for the period from
January 23, 1996 (inception) through December 31, 1996, with the historical
results of operations of Abacus for the six months ended June 30, 1999 and 1998,
and each of the three years ended December 31, 1998 and by combining the
unaudited pro forma condensed combined results of operations of DoubleClick and
Abacus for the six months ended June 30, 1999 and 1998, and each of the three
years ended December 31, 1998, with the historical results of operations of
NetGravity for the six months ended June 30, 1999 and 1998, and each of the
three years ended December 31, 1998, respectively, on a pooling of interests
basis.

    The unaudited pro forma condensed combined financial statements are based on
the estimates and assumptions set forth in the notes to these statements, which
are preliminary and have been made solely for purposes of developing this pro
forma information. The unaudited pro forma condensed combined financial
statements are not necessarily an indication of the results that would have been
achieved had these transactions been consummated as of the dates indicated or
that may be achieved in the future.

    DoubleClick and Abacus estimate that they will incur direct transaction
costs of approximately $16.0 million in connection with the proposed merger and
approximately $10.75 million for the proposed merger with NetGravity, which will
be charged to operations in the quarter in which the mergers are consummated.
The transaction costs consist of fees for investment bankers, attorneys,
accountants, financial printing and other related charges. We cannot assure you
that DoubleClick will not incur additional charges in subsequent quarters to
reflect costs associated with the proposed mergers.

    These unaudited pro forma condensed combined financial statements should be
read in conjunction with the historical consolidated financial statements and
related notes thereto and other financial information pertaining to DoubleClick,
Abacus and NetGravity, including "Management's Discussion and Analysis of
Financial Condition and Results of Operations" and "Risk Factors" incorporated
by reference in this joint proxy statement/prospectus.

                                       77
<PAGE>
                                DOUBLECLICK INC.
              UNAUDITED PRO FORMA CONDENSED COMBINED BALANCE SHEET
                              AS OF JUNE 30, 1999
                                 (IN THOUSANDS)

<TABLE>
<CAPTION>
                                                                                     DOUBLECLICK/
                                                                                       ABACUS/                     DOUBLECLICK/
                                                                                      NETGRAVITY                   NETGRAVITY/
                                                                                         PRO                          ABACUS
                                                                  HISTORICAL            FORMA                       PRO FORMA
                                                            ----------------------   ------------    HISTORICAL    ------------
                                                            DOUBLECLICK    ABACUS      COMBINED      NETGRAVITY      COMBINED
                                                            -----------   --------   ------------   ------------   ------------
<S>                                                         <C>           <C>        <C>            <C>            <C>
ASSETS
CURRENT ASSETS:
Cash, cash equivalents and short-term investments.........   $372,988     $23,563      $396,551       $125,043       $521,594
Accounts receivable, net..................................     20,351      14,857        35,208          9,231         44,439
Prepaid expenses and other current assets.................      2,033       3,301         5,334          1,909          7,243
                                                             --------     -------                     --------       --------
    Total current assets..................................    395,372      41,721       437,093        136,183        573,276
Property and equipment, net...............................     21,168       7,114        28,282          5,870         34,152
Investments and other assets..............................      5,801         146         5,947          1,655          7,602
                                                             --------     -------      --------       --------       --------
    Total assets..........................................   $422,341     $48,981      $471,322       $143,708       $615,030
                                                             ========     =======      ========       ========       ========

LIABILITIES AND STOCKHOLDERS' EQUITY
CURRENT LIABILITIES:
Accounts payable and accrued expenses.....................   $ 28,055     $ 5,756      $ 33,811       $  4,893       $ 38,704
Deferred revenues.........................................      6,482          --         6,482          7,791         14,273
Deferred license and service fees.........................        344          --           344             --            344
                                                             --------     -------      --------       --------       --------
    Total current liabilities.............................     34,881       5,756        40,637         12,684         53,321

Convertible subordinated notes............................    250,000          --       250,000             --        250,000
Other liabilities.........................................        295         447           742             --            742

STOCKHOLDERS' EQUITY:
Common stock..............................................         40          10            50             18             68
Additional paid-in capital................................    205,221      14,499       219,720        161,121        380,841
Accumulated earnings (deficit)............................    (67,253)     28,269       (38,984)       (28,849)       (67,833)
Deferred compensation.....................................       (265)         --          (265)        (1,266)        (1,531)
Other comprehensive income (loss).........................       (578)         --          (578)            --           (578)
                                                             --------     -------      --------       --------       --------
    Total stockholders' equity............................    137,165      42,778       179,943        131,024        310,967
                                                             --------     -------      --------       --------       --------
    Total liabilites and stockholders' equity.............   $422,341     $48,981      $471,322       $143,708       $615,030
                                                             ========     =======      ========       ========       ========
</TABLE>

    The accompanying notes are an integral part of these unaudited pro forma
                               condensed combined
                             financial statements.

                                       78
<PAGE>
                                DOUBLECLICK INC.

         UNAUDITED PRO FORMA CONDENSED COMBINED STATEMENT OF OPERATIONS

                         SIX MONTHS ENDED JUNE 30, 1999

                    (IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)

<TABLE>
<CAPTION>
                                                                                            DOUBLECLICK/
                                                                DOUBLECLICK/                  ABACUS/
                                                                   ABACUS                    NETGRAVITY
                                             HISTORICAL          PRO FORMA     HISTORICAL    PRO FORMA
                                       ----------------------   ------------   ----------   ------------
                                       DOUBLECLICK    ABACUS      COMBINED     NETGRAVITY     COMBINED
                                       -----------   --------   ------------   ----------   ------------
<S>                                    <C>           <C>        <C>            <C>          <C>
Revenues.............................    $ 53,079    $25,968      $79,047        10,221       $ 89,268
Cost of revenues.....................      25,038      6,463       31,501         4,796         36,297
                                         --------    -------      -------       -------       --------
  Gross profit.......................      28,041     19,505       47,546         5,425         52,971
                                         --------    -------      -------       -------       --------
Operating expenses:
  Sales and marketing................      25,059      8,142       33,201         6,898         40,099
  General and administrative.........       8,750      2,643       11,393         2,417         13,810
  Product development................       7,691      1,381        9,072         3,577         12,649
  Facility relocation & other........       2,132         --        2,132            --          2,132
                                         --------    -------      -------       -------       --------
    Total operating expenses.........      43,632     12,166       55,798        12,892         68,690
                                         --------    -------      -------       -------       --------
Income (loss) from operations........     (15,591)     7,339       (8,252)       (7,467)       (15,719)
Equity in losses of joint venture....          --       (365)        (365)           --           (365)
Interest and other net...............       3,055        567        3,622         1,615          5,237
                                         --------    -------      -------       -------       --------
Income (loss) before income taxes....     (12,536)     7,541       (4,995)       (5,852)       (10,847)
Provision for income taxes...........          --      2,964        2,964            --          2,964
                                         --------    -------      -------       -------       --------
Net income (loss)....................    $(12,536)   $ 4,577      $(7,959)      $(5,852)      $(13,811)
                                         ========    =======      =======       =======       ========

Net income (loss) per share--basic...    $  (0.32)   $  0.46      $ (0.16)      $ (0.38)      $  (0.25)
                                         --------    -------      -------       -------       --------
Net income (loss) per
  share--diluted.....................    $  (0.32)   $  0.44      $ (0.16)      $ (0.38)      $  (0.25)
                                         --------    -------      -------       -------       --------
Weighted average shares used in basic
  per share calculation..............      39,435      9,878       49,807        15,572         54,167
                                         --------    -------      -------       -------       --------
Weighted average shares used in
  diluted per share calculation......      39,435     10,475       49,807        15,572         54,167
                                         --------    -------      -------       -------       --------
</TABLE>

    The accompanying notes are an integral part of these unaudited pro forma
                    condensed combined financial statements.

                                       79
<PAGE>
                                DOUBLECLICK INC.

         UNAUDITED PRO FORMA CONDENSED COMBINED STATEMENT OF OPERATIONS

                         SIX MONTHS ENDED JUNE 30, 1998

                    (IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)

<TABLE>
<CAPTION>
                                                                                            DOUBLECLICK/
                                                                DOUBLECLICK/                  ABACUS/
                                                                   ABACUS                    NETGRAVITY
                                             HISTORICAL          PRO FORMA     HISTORICAL    PRO FORMA
                                       ----------------------   ------------   ----------   ------------
                                       DOUBLECLICK    ABACUS      COMBINED     NETGRAVITY     COMBINED
                                       -----------   --------   ------------   ----------   ------------
<S>                                    <C>           <C>        <C>            <C>          <C>
Revenues.............................    $ 30,297    $18,449      $48,746       $ 4,335       $ 53,081
Cost of revenues.....................      20,569      4,227       24,796         2,285         27,081
                                         --------    -------      -------       -------       --------
  Gross profit.......................       9,728     14,222       23,950         2,050         26,000
                                         --------    -------      -------       -------       --------
Operating expenses
  Sales and marketing................      12,508      5,936       18,444         4,395         22,839
  General and administrative.........       4,970      2,244        7,214         1,462          8,676
  Product development................       2,579        851        3,430         2,059          5,489
                                         --------    -------      -------       -------       --------
    Total operating expenses.........      20,057      9,031       29,088         7,916         37,004
                                         --------    -------      -------       -------       --------
Income (loss) from operations........     (10,329)     5,191       (5,138)       (5,866)       (11,004)
Interest and other net...............       1,228        305        1,533            56          1,589
                                         --------    -------      -------       -------       --------
Income (loss) before income taxes....      (9,101)     5,496       (3,605)       (5,810)        (9,415)
Provision for income taxes...........          --      2,006        2,006            --          2,006
                                         --------    -------      -------       -------       --------
Net Income (loss)....................    $ (9,101)   $ 3,490      $(5,611)      $(5,810)      $(11,421)
                                         --------    -------      -------       -------       --------

Net income (loss) per share--basic...    $  (0.34)   $  0.36      $ (0.15)      $ (1.42)      $  (0.30)
                                         --------    -------      -------       -------       --------
Net income (loss) per
  share--diluted.....................    $  (0.34)   $  0.34      $ (0.15)      $ (1.42)      $  (0.30)
                                         --------    -------      -------       -------       --------
Weighted average shares used in basic
  per share calculation..............      27,101      9,692       37,278         4,079         38,420
                                         --------    -------      -------       -------       --------
Weighted average shares used in
  diluted per share calculation......      27,101     10,202       37,278         4,079         38,420
                                         --------    -------      -------       -------       --------
</TABLE>

    The accompanying notes are an integral part of these unaudited pro forma
                    condensed combined financial statements.

                                       80
<PAGE>
                                DOUBLECLICK INC.

         UNAUDITED PRO FORMA CONDENSED COMBINED STATEMENT OF OPERATIONS

                          YEAR ENDED DECEMBER 31, 1998

                    (IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)

<TABLE>
<CAPTION>
                                                                                            DOUBLECLICK/
                                                                DOUBLECLICK/                  ABACUS/
                                                                   ABACUS                    NETGRAVITY
                                             HISTORICAL          PRO FORMA     HISTORICAL    PRO FORMA
                                       ----------------------   ------------   ----------   ------------
                                       DOUBLECLICK    ABACUS      COMBINED     NETGRAVITY     COMBINED
                                       -----------   --------   ------------   ----------   ------------
<S>                                    <C>           <C>        <C>            <C>          <C>
Revenues.............................    $ 80,188    $46,979      $127,167      $ 11,557      $138,724
Cost of revenues.....................      53,964      9,581        63,545         5,228        68,773
                                         --------    -------      --------      --------      --------
  Gross profit.......................      26,224     37,398        63,622         6,329        69,951
                                         --------    -------      --------      --------      --------
Operating expenses:
  Sales and marketing................      29,180     12,628        41,808        10,351        52,159
  General and administrative.........      11,288      4,928        16,216         3,172        19,388
  Product development................       6,684      1,691         8,375         4,639        13,014
  Facility relocation & other........          --        360           360            --           360
                                         --------    -------      --------      --------      --------
    Total operating expenses.........      47,152     19,607        66,759        18,162        84,921
                                         --------    -------      --------      --------      --------
Income (loss) from operations........     (20,928)    17,791        (3,137)      (11,833)      (14,970)

Equity in losses of joint venture....          --        (53)          (53)           --           (53)
Interest and other, net..............       2,756        754         3,510           540         4,050
                                         --------    -------      --------      --------      --------
Income (loss) before income taxes....     (18,172)    18,492           320       (11,293)      (10,973)
Provision for income taxes...........          --      7,066         7,066                       7,066
                                         --------    -------      --------      --------      --------
Net income (loss)....................    $(18,172)   $11,426      $ (6,746)     $(11,293)     $(18,039)
                                         ========    =======      ========      ========      ========

Net income (loss) per share--basic...    $  (0.60)   $  1.17      $  (0.17)     $  (1.28)     $  (0.42)
                                         --------    -------      --------      --------      --------
Net income (loss) per
  share--diluted.....................    $  (0.60)   $  1.12         (0.17)     $  (1.28)     $  (0.42)
                                         --------    -------      --------      --------      --------
Weighted average shares used in basic
  per share calculation..............      30,440      9,727        40,654         8,823        43,124
                                         --------    -------      --------      --------      --------
Weighted average shares used in
  diluted per share calculation......      30,440     10,216        40,654         8,823        43,124
                                         --------    -------      --------      --------      --------
</TABLE>

    The accompanying notes are an integral part of these unaudited pro forma
                    condensed combined financial statements.

                                       81
<PAGE>
                                DOUBLECLICK INC.

         UNAUDITED PRO FORMA CONDENSED COMBINED STATEMENT OF OPERATIONS

                          YEAR ENDED DECEMBER 31, 1997

                    (IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)

<TABLE>
<CAPTION>
                                                                                            DOUBLECLICK/
                                                                DOUBLECLICK/                  ABACUS/
                                                                   ABACUS                    NETGRAVITY
                                             HISTORICAL          PRO FORMA     HISTORICAL    PRO FORMA
                                       ----------------------   ------------   ----------   ------------
                                       DOUBLECLICK    ABACUS      COMBINED     NETGRAVITY     COMBINED
                                       -----------   --------   ------------   ----------   ------------
<S>                                    <C>           <C>        <C>            <C>          <C>
Revenues.............................    $30,597     $30,971      $61,568       $  6,358      $67,926
Cost of revenues.....................     20,628       5,942       26,570          2,572       29,142
                                         -------     -------      -------       --------      -------
  Gross profit.......................      9,969      25,029       34,998          3,786       38,784
                                         -------     -------      -------       --------      -------
Operating expenses:
  Sales and marketing................     10,710       8,000       18,710          6,073       24,783
  General and administrative.........      6,326       3,911       10,237          1,552       11,789
  Product development................      1,398       1,507        2,905          3,033        5,938
  Facility relocation & other........         --         102          102             --          102
                                         -------     -------      -------       --------      -------
    Total operating expenses.........     18,434      13,520       31,954         10,658       42,612
                                         -------     -------      -------       --------      -------
Income (loss) from operations........     (8,465)     11,509        3,044         (6,872)      (3,828)

Interest and other net...............        109         297          406            (10)         396
                                         -------     -------      -------       --------      -------
Income (loss) before income taxes....     (8,356)     11,806        3,450         (6,882)      (3,432)
Provision for income taxes...........         --       4,309        4,309             --        4,309
                                         -------     -------      -------       --------      -------
Net income (loss)....................    $(8,356)    $ 7,497      $  (859)      $ (6,882)     $(7,741)
                                         =======     =======      =======       ========      =======

Net income (loss) per share--basic...    $ (0.61)    $  0.78      $ (0.04)      $  (2.46)     $ (0.32)
Net income (loss) per
  share--diluted.....................    $ (0.61)    $  0.74      $ (0.04)      $  (2.46)     $ (0.32)

Weighted average shares used in basic
  per share calculation..............    $13,718     $ 9,546       23,740          2,799       24,524
Weighted average shares used in
  diluted per share calculation......    $13,718      10,058       23,740          2,799       24,524
</TABLE>

    The accompanying notes are an integral part of these unaudited pro forma
                    condensed combined financial statements.

                                       82
<PAGE>
                                DOUBLECLICK INC.

         UNAUDITED PRO FORMA CONDENSED COMBINED STATEMENT OF OPERATIONS

                          YEAR ENDED DECEMBER 31, 1996

                    (IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)

<TABLE>
<CAPTION>
                                                                                            DOUBLECLICK/
                                                                DOUBLECLICK/                  ABACUS/
                                                                   ABACUS                    NETGRAVITY
                                             HISTORICAL          PRO FORMA     HISTORICAL    PRO FORMA
                                       ----------------------   ------------   ----------   ------------
                                       DOUBLECLICK    ABACUS      COMBINED     NETGRAVITY     COMBINED
                                       -----------   --------   ------------   ----------   ------------
<S>                                    <C>           <C>        <C>            <C>          <C>
Revenues.............................    $ 6,514     $17,532      $24,046       $ 1,939       $25,985
Cost of revenues.....................      3,780       3,751        7,531           702         8,233
                                         -------     -------      -------       -------       -------
    Gross profit.....................      2,734      13,781       16,515         1,237        17,752
                                         -------     -------      -------       -------       -------
Operating expenses:
  Sales and marketing................      3,079       4,294        7,373         2,839        10,212
  General and administrative.........      2,145       2,204        4,349         1,315         5,664
  Product development................        618         913        1,531         1,764         3,295
                                         -------     -------      -------       -------       -------
    Total operating expenses.........      5,842       7,411       13,253         5,918        19,171
                                         -------     -------      -------       -------       -------
Income (loss) from operations........     (3,108)      6,370        3,262        (4,681)       (1,419)

Interest and others, net.............        (84)       (116)        (200)           54          (146)
                                         -------     -------      -------       -------       -------
Income (loss) before income taxes....     (3,192)      6,254        3,062        (4,627)       (1,565)
Provision for income taxes...........         --       2,389        2,389            --         2,389
                                         -------     -------      -------       -------       -------

Net income (loss)....................    $(3,192)    $ 3,865      $   673       $(4,627)      $(3,954)
                                         =======     =======      =======       =======       =======

Net income (loss) per share--basic...    $ (0.18)    $  0.43      $  0.02       $ (2.19)      $ (0.14)
                                         -------     -------      -------       -------       -------
Net income (loss) per
  share--diluted.....................    $ (0.18)    $  0.40      $  0.02       $ (2.19)      $ (0.14)
                                         -------     -------      -------       -------       -------

Weighted average shares used in basic
  per share calculation..............     18,118       9,094       27,667         2,111        28,258
Weighted average shares used in
  diluted per share calculation......     18,118       9,614       28,213         2,111        28,258
</TABLE>

    The accompanying notes are an integral part of these unaudited pro forma
                    condensed combined financial statements.

                                       83
<PAGE>
                     NOTES TO UNAUDITED PRO FORMA CONDENSED

                         COMBINED FINANCIAL STATEMENTS

NOTE 1

    The unaudited pro forma condensed combined financial statements of
DoubleClick and Abacus give retroactive effect to the proposed merger of
DoubleClick and Abacus, which is expected to be accounted for as a pooling of
interests and, as a result, the unaudited pro forma condensed combined balance
sheet and statements of operations are presented as if DoubleClick and Abacus
had been combined for all periods presented. On July 12, 1999, DoubleClick
entered into an agreement to merge with NetGravity. The unaudited pro forma
condensed combined financial statements of DoubleClick and Abacus have been
updated to reflect the proposed merger with NetGravity, which is expected to be
accounted for as a pooling of interests and, as a result, the unaudited pro
forma condensed combined balance sheet and statements of operations are
presented as if DoubleClick, Abacus and NetGravity had been combined for all
periods presented.

    The unaudited pro forma condensed combined financial statements, including
the related notes, should be read in conjunction with the historical
consolidated financial statements and related notes of DoubleClick, Abacus and
NetGravity which are incorporated by reference in this joint proxy statement/
prospectus. Amounts from the Abacus and NetGravity historical consolidated
financial statements have been reclassified in the unaudited pro forma condensed
combined financial statements to conform with DoubleClick historical
classifications.

    All share numbers in these unaudited pro forma condensed combined financial
statements for all periods presented have been adjusted to reflect the
DoubleClick 2-for-1 stock split that occurred in April 1999.

NOTE 2

    Basic net income (loss) per share is computed using the weighed average
number of common shares outstanding during the period. Diluted net income (loss)
per share is computed using the weighed average number of common and dilutive
common equivalent shares outstanding during the period. Dilutive common
equivalent shares consist of the incremental common shares issuable upon
conversion of convertible preferred stock, convertible notes (using the
if-converted method), and shares issuable upon exercise of stock options (using
the treasury stock method). Common equivalent shares or shares issuable upon
conversion of potentially dilutive securities are excluded from the computations
if their effect is anti-dilutive. Pro forma net income (loss) per share is
computed by adding DoubleClick historical weighted average shares outstanding to
Abacus and NetGravity historical weighted average shares outstanding converted
to give effect to the exchange ratio of 1.05 and 0.28, respectively.

NOTE 3

    The provision for income taxes does not reflect the benefit of DoubleClick's
or NetGravity's net losses due to limitations and uncertainty surrounding
realization.

NOTE 4

    It is anticipated that the combined company will incur estimated direct
transaction charges of $16 million related to the proposed merger of DoubleClick
with Abacus and $10.75 million for the NetGravity merger, principally in the
quarter in which the proposed merger is consummated. These charges include
estimated investment banking and financial advisory fees of approximately
$12.5 million and $7.25 million for the Abacus and NetGravity merger,
respectively, and other estimated merger related expenses totaling $3.5 million
for each of the Abacus and NetGravity mergers consisting primarily of other
professional services and estimated registration expenses. These anticipated
charges are preliminary estimates and are subject to change. Actual amounts
ultimately incurred could differ from the estimated amounts. The actual amounts
will be charged to the statement of operations in the period the transaction is
consummated. Additionally, the direct transaction charges do not include
integration costs which may be incurred as of and subsequent to the mergers.
Neither DoubleClick, Abacus or NetGravity have estimated the amount or nature of
integration costs.

                                       84
<PAGE>
                       COMPARISON OF RIGHTS OF HOLDERS OF
                            ABACUS COMMON STOCK AND
                            DOUBLECLICK COMMON STOCK

    This section of the joint proxy statement/prospectus describes certain
differences between the rights of holders of Abacus common stock and DoubleClick
common stock. While we believe that the description covers the material
differences between the two, this summary may not contain all of the information
that is important to you. You should carefully read this entire document and the
other documents we refer to for a more complete understanding of the differences
between being a stockholder of Abacus and being a stockholder of DoubleClick.

    The rights of the stockholders of Abacus are governed by Abacus's
Certificate of Incorporation, as currently in effect, and Abacus's Bylaws. After
completion of the merger, Abacus stockholders will become stockholders of
DoubleClick and their rights will be governed by DoubleClick's Amended and
Restated Certificate of Incorporation and its Amended and Restated Bylaws. Both
companies are incorporated under the laws of the State of Delaware and,
accordingly, Abacus stockholders rights will continue to be governed by the
Delaware General Corporation Law after completion of the merger.

CLASSES OF COMMON STOCK OF ABACUS AND DOUBLECLICK

    Both DoubleClick and Abacus have one class of common stock issued and
outstanding. Holders of DoubleClick common stock and Abacus common stock are
each entitled to one vote for each share held.

CLASSIFIED BOARD OF DIRECTORS

    Delaware law provides that a corporation's board of directors may be divided
into various classes with staggered terms of office. DoubleClick's board of
directors is divided into three classes, as nearly equal in size as possible,
with one class being elected annually for a three-year term. DoubleClick
directors are elected for a term of three years and until their successors are
elected and qualified.

    Abacus's directors are elected at the annual meeting of the stockholders and
hold office until the next annual meeting and until their successors are elected
and qualified.

NUMBER OF DIRECTORS

    DoubleClick's board of directors may consist of not fewer than five nor more
than fifteen directors and currently consists of seven directors. The range of
directors on DoubleClick's board may be changed only by a vote of 66.67% of the
outstanding shares of the capital stock of DoubleClick at a special meeting of
the stockholders called for that purpose.

    Abacus's board of directors may consist of not fewer than two nor more than
twelve directors, and currently consists of five directors. The number of
directors is determined by resolution of the Board of Directors.

REMOVAL OF DIRECTORS

    DoubleClick directors, or the entire DoubleClick board, may be removed, at
any time, but only for cause and only by the affirmative vote of the holders of
at least 66.67% of the outstanding shares of capital stock of DoubleClick
entitled to vote generally in the election of directors, voting together as a
single class, cast at a special meeting of the stockholders called for that
purpose.

    Abacus directors, or the entire Abacus board, may be removed, at any time,
with or without cause, by the affirmative vote of the holders of a majority of
the shares then entitled to vote on the election of directors.

                                       85
<PAGE>
FILLING VACANCIES ON THE BOARD OF DIRECTORS

    Any newly created directorships in DoubleClick's board resulting from any
increase in the number of authorized directors or any vacancies, may be filled
by 66.67% of the directors then in office, though less than a quorum, or be a
sole remaining director.

    In the case of DoubleClick, any director chosen in this manner to fill a
vacancy holds office until the annual meeting of stockholders at which the term
of the class to which that director has been chosen expires and until that
director's successor is elected and qualified.

    Any newly created directorships in Abacus's board of directors resulting
from any increase in the number of authorized directors or any vacancies, may be
filled by a majority of the remaining members of the board of directors, even
though less than a quorum, or by the sole remaining director.

ABILITY TO CALL SPECIAL MEETINGS

    Special meetings of stockholders of DoubleClick may be called by the
President or by the Secretary at the written request of two-thirds of the Board
of Directors upon not fewer than 10 or more than 60 days' written notice.

    Special meetings of Abacus stockholders may be called at any time but only
by

    - its President,

    - its Chairman of the Board,

    - a majority of the directors in office, or

    - a majority of the stockholders holding voting stock.

ADVANCE NOTICE PROVISIONS FOR STOCKHOLDER NOMINATIONS AND PROPOSALS

    At an annual meeting of DoubleClick stockholders, only business as has been
properly brought before the meeting will be conducted. To be properly brought
before an annual meeting of DoubleClick, business must be:

    - provided in DoubleClick's notice of meeting,

    - otherwise properly brought before the meeting by or at the direction of
      the board, or

    - otherwise properly brought before the meeting by a stockholder.

    For business to be properly brought before an annual DoubleClick meeting by
a stockholder, the stockholder must have given timely notice thereof in writing
to the Secretary of DoubleClick. To be timely, a stockholder's notice must be
delivered to or mailed and received at the principal executive offices of
DoubleClick not later than the close of business on the 120th day or earlier
than the close of business on the 150th day prior to the first anniversary of
the proxy statement delivered to stockholders in connection with the preceding
year's annual meeting; provided, however, that if either (A) the date of the
annual meeting is more than 30 days before or more than 60 days after this
anniversary date or (B) no proxy statement was delivered to stockholders in
connection with the preceding year's annual meeting, notice by the stockholder,
to be timely, must be delivered not earlier than the close of business on the
90th day prior to the annual meeting and not later than the close of business on
the later of the 60th day prior to the annual meeting or the close of business
on the tenth day following the day on which public announcement of the date of
the meeting is first made by DoubleClick.

    If, however, the number of directors to be elected to the DoubleClick board
is increased and there is no public announcement by DoubleClick naming all of
the nominees for director or specifying the size of the increased Board at least
70 days prior to the first anniversary of the preceding year's annual meeting
(or, if the annual meeting is held more than 30 days before or 60 days after the
anniversary date, at least 70 days prior to the annual meeting), notice by the
stockholder will be considered timely (but only with respect to nominees for any
new positions created by the increase in number of the Board of Directors) if

                                       86
<PAGE>
it is delivered no later than the close of business on the tenth day following
the day on which public announcement of the date of the meeting is first made by
DoubleClick.

    A stockholder's notice to the Secretary must set forth:

    - as to each person whom the stockholder proposes to nominate for election
      or reelection as a director, all information relating to the person that
      is required to be disclosed in solicitations of proxies for election of
      directors, or is otherwise required, in each case under Regulation 14A
      under the Exchange Act (including the person's written consent to being
      named in the proxy statement as a nominee and to serving as a director it
      elected);

    - as to any other business that the stockholder proposes to bring before the
      meeting, a brief description of the business desired to be brought before
      the meeting, the reasons for conducting this business at the meeting and
      any material interest in the business of the stockholder and the
      beneficial owner, if any, on whose behalf the proposal is made; and

    - as to the stockholder giving the notice and the beneficial owner, if any,
      on whose behalf the nomination or proposal is made (A) the name and
      address of the stockholder, as they appear on DoubleClick's books, and of
      the beneficial owner and (B) the class and number of shares of capital
      stock of DoubleClick that are owned beneficially and held of record by the
      stockholder and the beneficial owner.

    Nominations of persons for election to the DoubleClick board may be made at
a meeting of stockholders at which directors are to be elected in accordance
with DoubleClick's notice of meeting (A) by or at the direction of the board or
(B) provided that the board has determined that directors will be elected at the
meeting, by any stockholder of the corporation entitled to vote in the election
of directors at the meeting who complies with DoubleClick's notice procedures.
These nominations, other than those made by or at the direction of the board,
must be made with timely notice in writing to the Secretary of DoubleClick. If
DoubleClick calls a special meeting of stockholders for the purpose of electing
one or more directors to the board, any stockholder may nominate a person or
persons, for election to the position(s) as specified in DoubleClick's notice of
meeting, if the stockholder's notice is delivered to the Secretary not earlier
than the 90th day prior to the special meeting and not later than the later of
(i) the close of business of the 60th day prior to the special meeting or
(ii) the close of business of the 10th day following the day on which public
announcement is first made of the date of the special meeting and of the
nominees proposed by the board to be elected at the meeting.

    Abacus's Bylaws are silent as to the matter of stockholder proposals.

AMENDMENT OF CERTIFICATE OF INCORPORATION

    Under Delaware law, a certificate of incorporation of a Delaware corporation
may be amended by approval of the board of directors of the corporation and the
affirmative vote of the holders of a majority of the outstanding shares entitled
to vote for the amendment, unless a higher vote is required by the corporation's
certificate of incorporation.

    DoubleClick's certificate of incorporation provides that the affirmative
vote of the holders of at least 66.67% of the outstanding shares of capital
stock of DoubleClick entitled to vote generally in the election of directors,
voting together as a single class, are required to alter, change, amend, repeal
or adopt any provision inconsistent with the provisions of DoubleClick's
certificate of incorporation that deal with the following:

    - matters relating to the board of directors, including the number of
      members, board classification, vacancies and removal;

    - the manner in which stockholder action may be effected;

    - limitation of the liability of DoubleClick's directors;

    - indemnification of DoubleClick's directors and officers;

                                       87
<PAGE>
    - amendments to DoubleClick's bylaws; and

    - amendments to DoubleClick's certificate of incorporation.

    Abacus's Certificate of Incorporation may be amended in accordance with the
Delaware General Corporation Law.

AMENDMENT OF BYLAWS

    Under Delaware law, stockholders entitled to vote have the power to adopt,
amend or repeal bylaws. In addition, a corporation may, in its certificate of
incorporation, confer this power upon the board of directors. The stockholders
always have the power to adopt, amend or repeal bylaws, even though the board
may also be delegated this power.

    The DoubleClick Amended and Restated Bylaws may be altered, amended or
repealed, or new bylaws may be adopted, by the affirmative vote of (A) at least
66.67% of the board or (B) the holders of at least 66.67% of the outstanding
shares of capital stock of DoubleClick entitled to vote generally in the
election of directors, voting together as a single class, which votes are cast
at a special meeting of the stockholders called for that purpose.

    The Abacus Bylaws may be adopted, amended or repealed, or new bylaws may be
adopted, by the affirmative vote of either a majority of the outstanding capital
stock entitled to vote or a majority of the entire board then in office.

INDEMNIFICATION OF DIRECTORS AND OFFICERS

    The Delaware General Corporation Law permits a corporation to indemnify
officers and directors for actions taken in good faith and in a manner they
reasonably believed to be in, or not opposed to, the best interests of the
corporation, and with respect to any criminal action that they had no reasonable
cause to believe was unlawful.

    Our certificates of incorporation and bylaws provide that any person who was
or is a party or is threatened to be a party to or is involved in any action,
suit, or proceeding, whether civil, criminal, administrative or investigative,
because that person is or was a director or officer, or is or was serving at the
request of either of us as a director, officer, employee or agent of another
corporation or of a partnership, joint venture, trust or other enterprise, will
be indemnified against expenses (including attorney's fees), judgments, fines
and amounts paid in settlement reasonably incurred by the indemnified person or
on his behalf in connection with the action, suit or proceeding and any appeal
therefrom, and held harmless by each of us to the fullest extent permitted by
the Delaware General Corporation Law. The indemnification rights conferred by
each of us are not exclusive of any other right to which persons seeking
indemnification may be entitled under any statute, our certificates of
incorporation or bylaws, any agreement, vote of stockholders or disinterested
directors or otherwise.

    Additionally, DoubleClick may pay expenses incurred by its directors or
officers in defending a civil or criminal action, suit or proceeding because
that person is a director or officer, in advance of the final disposition of
that action, suit or proceeding. These payments will be made however only if
DoubleClick receives an undertaking by or on behalf of that director or officer
to repay all amounts advanced if it is ultimately determined that he or she is
not entitled to be indemnified by DoubleClick, as authorized by the Delaware
General Corporation Law. Abacus maintains indemnification agreements with its
officers and directors.

                                       88
<PAGE>
                                    EXPERTS

    The consolidated balance sheets of DoubleClick Inc. as of as of
December 31, 1998 and 1997 and the consolidated statements of operations,
shareholders' equity, and cash flows for each of the two years in the period
ended December 31, 1998, and for the period from January 23, 1996 (inception)
through December 31, 1996, incorporated in this joint proxy
statement/prospectus, by reference to the Annual Report on Form 10-K of
DoubleClick Inc., as amended on April 27, 1999, for the year ended December 31,
1998, have been so incorporated in reliance on the report of
PricewaterhouseCoopers LLP, independent accountants, given on the authority of
that firm as experts in accounting and auditing.

    The consolidated financial statements of Abacus Direct Corporation as of
December 31, 1998 and 1997 and for each of the three years in the period ended
December 31, 1998, incorporated in this joint proxy statement/prospectus by
reference to the Annual Report on Form 10-K of Abacus Direct Corporation for the
year ended December 31, 1998, have been so incorporated in reliance on the
report of PricewaterhouseCoopers LLP, independent accountants, given on the
authority of that firm as experts in accounting and auditing.

    The consolidated financial statements of NetGravity, Inc. as of
December 31, 1998 and 1997 and for each of the years in the three-year period
ended December 31, 1998, have been incorporated by reference in this joint proxy
statement/prospectus by reference to the Annual Report on Form 10-K of
NetGravity, Inc. for the year ended December 31, 1998, in reliance on the report
of KPMG LLP, independent certified accountants, upon the authority of said firm
as experts in auditing and accounting.

                                 LEGAL MATTERS

    The validity of the shares of DoubleClick common stock offered by this joint
proxy statement/ prospectus and the federal income tax consequences in
connection with the merger will be passed upon for DoubleClick by Brobeck,
Phleger & Harrison LLP, New York, New York. Legal matters pertaining to federal
income tax consequences in connection with the merger will be passed upon for
Abacus by Parker Chapin Flattau & Klimpl, LLP, New York, New York.

                      WHERE YOU CAN FIND MORE INFORMATION

    DoubleClick, Abacus and NetGravity file annual, quarterly and special
reports, proxy statements and other information with the Securities and Exchange
Commission. Stockholders may read and copy any reports, statements or other
information filed by DoubleClick, Abacus or NetGravity at the Commission's
public reference rooms in Washington, D.C., New York, New York and Chicago,
Illinois. Please call the Commission at 1-800-SEC-0330 for further information
on the public reference rooms. DoubleClick's, Abacus's and NetGravity's filings
with the Commission are also available to the public from commercial
document-retrieval services and at the Web site maintained by the Commission at
http://www.sec.gov.

    DoubleClick has filed a registration statement with the Commission to
register the DoubleClick common stock to be issued to Abacus stockholders in the
merger. This joint proxy statement/prospectus is a part of that registration
statement and constitutes a proxy statement and prospectus of DoubleClick in
addition to being a proxy statement of Abacus for use at its special meeting.

    As allowed by the Commission's rules, this joint proxy statement/prospectus
does not contain all of the information relating to DoubleClick, Abacus and
NetGravity included in the registration statement or the exhibits to the
registration statement. Some of the important business and financial information
relating to DoubleClick, Abacus and NetGravity that may be important in deciding
how to vote is not included in this joint proxy statement/prospectus, but rather
is "incorporated by reference" to documents that have been previously filed by
DoubleClick, Abacus and NetGravity with the Commission. The information
incorporated by reference is deemed to be a part of this joint proxy
statement/prospectus, except for any

                                       89
<PAGE>
information superseded by information contained directly in this joint proxy
statement/prospectus. See "Incorporation of Documents by Reference."

    DoubleClick has supplied all information contained or incorporated by
reference in this joint proxy statement/prospectus relating to DoubleClick, and
Abacus has supplied all information contained or incorporated by reference in
this joint proxy statement/prospectus relating to Abacus.

    Stockholders can obtain any of the documents incorporated by reference
through DoubleClick, Abacus, NetGravity or the Commission. Documents
incorporated by reference are available from DoubleClick, Abacus and NetGravity
without charge, excluding all exhibits. Stockholders may obtain documents
incorporated by reference in this joint proxy statement/prospectus by requesting
them orally or in writing to the following addresses or by telephone:

<TABLE>
<S>                            <C>                                       <C>
DoubleClick Inc.               Abacus:                                   NetGravity, Inc.
Investor Relations             D. F. King & Co., Inc.                    Investor Relations
41 Madison Avenue, 32nd Floor  77 Water Street, 20th Floor               1900 S. Norfolk Street, Suite 150
New York, New York 10010       New York, New York 10005                  San Mateo, California 94403-1151
(212) 683-0001                 (800) 769-6414                            (650) 425-5960
</TABLE>

    If you would like to request documents, please do so by November 16, 1999 in
order to receive them before the special meetings.

    DOUBLECLICK STOCKHOLDERS SHOULD RELY ONLY ON THE INFORMATION CONTAINED IN OR
INCORPORATED BY REFERENCE IN THIS JOINT PROXY STATEMENT/PROSPECTUS TO VOTE ON
THE ISSUANCE OF DOUBLECLICK COMMON STOCK AS CONTEMPLATED BY THE MERGER
AGREEMENT. ABACUS STOCKHOLDERS SHOULD RELY ONLY ON THE INFORMATION CONTAINED IN
OR INCORPORATED BY REFERENCE IN THIS JOINT PROXY STATEMENT/PROSPECTUS TO VOTE ON
THE MERGER AGREEMENT AND THE MERGER. NEITHER DOUBLECLICK NOR ABACUS HAS
AUTHORIZED ANYONE TO PROVIDE INFORMATION THAT IS DIFFERENT FROM WHAT IS
CONTAINED IN THIS JOINT PROXY STATEMENT/PROSPECTUS. THIS JOINT PROXY STATEMENT/
PROSPECTUS IS DATED OCTOBER 21, 1999. STOCKHOLDERS SHOULD NOT ASSUME THAT THE
INFORMATION CONTAINED IN THIS JOINT PROXY STATEMENT/PROSPECTUS IS ACCURATE AS OF
ANY OTHER DATE, AND NEITHER THE MAILING OF THIS JOINT PROXY STATEMENT/PROSPECTUS
TO STOCKHOLDERS NOR THE ISSUANCE OF DOUBLECLICK COMMON STOCK IN THE MERGER SHALL
CREATE ANY IMPLICATION TO THE CONTRARY.

                    INCORPORATION OF DOCUMENTS BY REFERENCE

    The Commission allows us to "incorporate by reference" the information we
file with it, which means that we can disclose important information to you by
referring you to those documents. The information incorporated by reference is
considered to be part of this joint proxy statement/prospectus, and later
information filed with the Commission will update and supersede this
information. This joint proxy statement/prospectus incorporates by reference the
documents set forth below that DoubleClick, Abacus and NetGravity have
previously filed with the Commission. The documents contain important
information about DoubleClick, Abacus and NetGravity and their finances.

                                       90
<PAGE>
We incorporate by reference DoubleClick's:

    - Annual Report on Form 10-K, as amended by Annual Report on Form 10-K/A,
      for the year ended December 31, 1998;

    - Quarterly Reports on Form 10-Q, as amended by Quarterly Reports on Form
      10-Q/A, for the quarters ended March 31, 1999 and June 30, 1999;

    - Proxy Statement for DoubleClick's Annual Meeting of Stockholders held on
      May 24, 1999;

    - Reports on Form 8-K dated February 3, 1999, March 15, 1999, March 15,
      1999, June 17, 1999 and July 21, 1999; and

    - The description of DoubleClick common stock contained in DoubleClick's
      Registration Statement on Form 8-A dated November 30, 1998 registering the
      DoubleClick common stock under Section 12(g) of the Exchange Act.

    We also incorporate by reference Abacus's:

    - Annual Report on Form 10-K for the year ended December 31, 1998;

    - Quarterly Reports on Form 10-Q for the quarters ended March 31, 1999 and
      June 30, 1999;

    - Report on Form 8-K dated June 18, 1999; and

    - The description of Abacus common stock contained in Abacus's Registration
      Statement on Form 8-A dated September 24, 1996 registering the Abacus
      common stock under Section 12(g) of the Exchange Act.

    In addition, all of DoubleClick's and Abacus's filings with the Commission
after the date of this joint proxy statement/prospectus under Section 13(a),
13(c), 14 or 15(d) of the Exchange Act shall be deemed to be incorporated by
reference until the merger becomes effective.

    We also incorporate by reference:

    - Item 6 and Item 8 of Part I of NetGravity's Annual Report on Form 10-K for
      the year ended December 31, 1998;

    - Item 1 of Part I of NetGravity's Quarterly Report on Form 10-Q for the
      quarter ended March 31, 1999; and

    - Item 1 of Part I of NetGravity's Quarterly report on Form 10-Q, as amended
      by the quarterly report on Form 10-Q/A, for the quarter ended June 30,
      1999.

    In addition, all of the financial information contained in NetGravity's
filings with the Commission after the date of this joint proxy
statement/prospectus under Section 13(a), 13(c), 14 or 15(d) of the Exchange Act
shall be deemed to be incorporated by reference until the merger of NetGravity
and DoubleClick becomes effective.

    Any statement contained in this joint proxy statement/prospectus or in a
document incorporated or deemed to be incorporated by reference in this joint
proxy statement/prospectus shall be deemed to be modified or superseded for
purposes of this joint proxy statement/prospectus to the extent that a statement
contained in this or in any other later filed document which also is or is
deemed to be incorporated by reference modifies or supersedes the statement. Any
statement so modified or superseded shall not be deemed, except as so modified
or superseded, to constitute a part of this joint proxy statement/prospectus.

                                       91
<PAGE>
                                                                      APPENDIX A

                AGREEMENT AND PLAN OF MERGER AND REORGANIZATION
                                     AMONG
                               DOUBLECLICK INC.,
                              ATLANTA MERGER CORP.
                                      AND
                           ABACUS DIRECT CORPORATION
                           DATED AS OF JUNE 13, 1999
<PAGE>
                               TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                            PAGE
                                                                                          --------
<S>          <C>            <C>                                                           <C>
ARTICLE I DEFINITIONS...................................................................     A-1
             SECTION 1.01   Certain Defined Terms.......................................     A-1

ARTICLE II THE MERGER...................................................................     A-4
             SECTION 2.01   The Merger..................................................     A-4
             SECTION 2.02   Closing.....................................................     A-5
             SECTION 2.03   Effective Time..............................................     A-5
             SECTION 2.04   Effect of the Merger........................................     A-5
             SECTION 2.05   Certificate of Incorporation; Bylaws; Directors and Officers
                              of Surviving Corporation..................................     A-5

ARTICLE III CONVERSION OF SECURITIES; EXCHANGE OF CERTIFICATES..........................     A-5
             SECTION 3.01   Conversion of Shares........................................     A-5
             SECTION 3.02   Exchange of Shares Other than Treasury Shares...............     A-6
             SECTION 3.03   Stock Transfer Books........................................     A-7
             SECTION 3.04   No Fractional Share Certificates............................     A-8
             SECTION 3.05   Options to Purchase Company Common Stock....................     A-8
             SECTION 3.06   Unvested Stock..............................................     A-9
             SECTION 3.07   Certain Adjustments.........................................     A-9

ARTICLE IV REPRESENTATIONS AND WARRANTIES OF COMPANY....................................     A-9
             SECTION 4.01   Organization and Qualification; Subsidiaries................     A-9
             SECTION 4.02   Certificate of Incorporation and Bylaws.....................    A-10
             SECTION 4.03   Capitalization..............................................    A-10
             SECTION 4.04   Authority Relative to This Agreement........................    A-10
             SECTION 4.05   No Conflict; Required Filings and Consents..................    A-11
             SECTION 4.06   Permits; Compliance with Laws...............................    A-11
             SECTION 4.07   SEC Filings; Financial Statements...........................    A-11
             SECTION 4.08   Absence of Certain Changes or Events........................    A-12
             SECTION 4.09   Employee Benefit Plans; Labor Matters.......................    A-13
             SECTION 4.10   Pooling; Certain Tax Matters................................    A-15
             SECTION 4.11   Contracts...................................................    A-15
             SECTION 4.12   Litigation..................................................    A-15
             SECTION 4.13   Environmental Matters.......................................    A-16
             SECTION 4.14   Intellectual Property.......................................    A-16
             SECTION 4.15   Taxes.......................................................    A-18
             SECTION 4.16   Insurance...................................................    A-19
             SECTION 4.17   Properties..................................................    A-19
             SECTION 4.18   Affiliates..................................................    A-19
             SECTION 4.19   Opinion of Financial Advisor................................    A-20
             SECTION 4.20   Brokers.....................................................    A-20
             SECTION 4.21   Certain Business Practices..................................    A-20
             SECTION 4.22   Section 203 of the DGCL Not Applicable......................    A-20
             SECTION 4.23   Business Activity Restriction...............................    A-20

ARTICLE V REPRESENTATIONS AND WARRANTIES OF PARENT......................................    A-20
             SECTION 5.01   Organization and Qualification; Subsidiaries................    A-21
             SECTION 5.02   Certificate of Incorporation and Bylaws.....................    A-21
             SECTION 5.03   Capitalization..............................................    A-21
             SECTION 5.04   Authority Relative to this Agreement........................    A-22
</TABLE>

                                      A-i
<PAGE>

<TABLE>
<CAPTION>
                                                                                            PAGE
                                                                                          --------
<S>          <C>            <C>                                                           <C>
             SECTION 5.05   No Conflict; Required Filings and Consents..................    A-22
             SECTION 5.06   SEC Filings; Financial Statements...........................    A-22
             SECTION 5.07   Pooling; Certain Tax Matters................................    A-23
             SECTION 5.08   Opinion of Financial Advisor................................    A-23
             SECTION 5.09   Brokers.....................................................    A-23
             SECTION 5.10   Affiliates..................................................    A-23
             SECTION 5.11   No Parent Material Adverse Effect...........................    A-23

ARTICLE VI COVENANTS....................................................................    A-24
             SECTION 6.01   Conduct of Business by Company Pending the Closing..........    A-24
             SECTION 6.02   Notices of Certain Events...................................    A-25
             SECTION 6.03   Access to Information; Confidentiality......................    A-26
             SECTION 6.04   No Solicitation of Transactions.............................    A-26
             SECTION 6.05   Tax-Free Transaction; Pooling...............................    A-27
             SECTION 6.06   Control of Operations.......................................    A-27
             SECTION 6.07   Further Action; Consents; Filings...........................    A-27
             SECTION 6.08   Additional Reports..........................................    A-28
             SECTION 6.09   Tax Information.............................................    A-28
             SECTION 6.10   Conduct of Business by Parent...............................    A-28

ARTICLE VII ADDITIONAL AGREEMENTS.......................................................    A-28
             SECTION 7.01   Registration Statement; Joint Proxy Statement...............    A-28
             SECTION 7.02   Stockholders' Meetings......................................    A-30
             SECTION 7.03   Affiliates..................................................    A-30
             SECTION 7.04   Directors' and Officers' Indemnification and Insurance......    A-31
             SECTION 7.05   No Shelf Registration.......................................    A-31
             SECTION 7.06   Public Announcements........................................    A-32
             SECTION 7.07   NNM Listing.................................................    A-32
             SECTION 7.08   Blue Sky....................................................    A-32
             SECTION 7.09   Employee Benefit Matters....................................    A-32

ARTICLE VIII CONDITIONS TO THE MERGER...................................................    A-32
             SECTION 8.01   Conditions to the Obligations of Each Party to Consummate
                              the Merger................................................    A-32
             SECTION 8.02   Conditions to the Obligations of Company....................    A-33
             SECTION 8.03   Conditions to the Obligations of Parent.....................    A-33

ARTICLE IX TERMINATION, AMENDMENT AND WAIVER............................................    A-34
             SECTION 9.01   Termination.................................................    A-34
             SECTION 9.02   Effect of Termination.......................................    A-35
             SECTION 9.03   Amendment...................................................    A-35
             SECTION 9.04   Waiver......................................................    A-35
             SECTION 9.05   Termination Fee; Expenses...................................    A-36

ARTICLE X GENERAL PROVISIONS............................................................    A-37
             SECTION 10.01  Non-Survival of Representations and Warranties..............    A-37
             SECTION 10.02  Notices.....................................................    A-37
             SECTION 10.03  Severability................................................    A-38
             SECTION 10.04  Assignment; Binding Effect; Benefit.........................    A-38
             SECTION 10.05  Incorporation of Exhibits...................................    A-38
             SECTION 10.06  Governing Law...............................................    A-38
             SECTION 10.07  Waiver of Jury Trial........................................    A-39
</TABLE>

                                      A-ii
<PAGE>

<TABLE>
<CAPTION>
                                                                                            PAGE
                                                                                          --------
<S>          <C>            <C>                                                           <C>
             SECTION 10.08  Headings; Interpretation....................................    A-39
             SECTION 10.09  Counterparts................................................    A-39
             SECTION 10.10  Entire Agreement............................................    A-39
</TABLE>

                                     A-iii
<PAGE>
                AGREEMENT AND PLAN OF MERGER AND REORGANIZATION

    AGREEMENT AND PLAN OF MERGER AND REORGANIZATION, dated as of June 13, 1999
(as amended, supplemented or otherwise modified from time to time, this
"Agreement"), among DOUBLECLICK INC., a Delaware corporation ("Parent"), ABACUS
DIRECT CORPORATION, a Delaware corporation ("Company"), and ATLANTA MERGER
CORP., a Delaware corporation and a direct wholly owned subsidiary of Parent
("Merger Sub"):

                              W I T N E S S E T H:

    WHEREAS, the boards of directors of Parent and Company have determined that
it is advisable and in the best interests of their respective companies and
stockholders to enter into a business combination by means of the merger of
Merger Sub with and into Company (the "Merger") and have approved and adopted
this Agreement;

    WHEREAS, concurrently with the execution of this Agreement and as an
inducement to Parent to enter into this Agreement, certain stockholders of
Company have entered into a stockholder agreement (each, a "Stockholder
Agreement") in the form attached hereto as Annex A;

    WHEREAS, concurrently with the execution of this Agreement and as an
inducement to Parent to enter into this Agreement, Company has entered into an
option agreement (the "Option Agreement") in the form attached hereto as Annex
B;

    WHEREAS, upon the terms and subject to the conditions of this Agreement and
in accordance with the General Corporation Law of the State of Delaware (the
"DGCL"), Parent will acquire all of the common stock of Company through the
merger of Merger Sub with and into Company;

    WHEREAS, for financial reporting purposes, it is intended that the Merger be
accounted for as a "pooling of interests" under United States generally accepted
accounting principles ("U. S. GAAP") and the accounting standards of the United
States Securities and Exchange Commission (the "SEC"); and

    WHEREAS, for United States Federal income tax purposes, it is intended that
the Merger shall qualify as a tax-free reorganization under Section 368(a) of
the Internal Revenue Code of 1986, as amended (together with the rules and
regulations promulgated thereunder, the "Code"), and that this Agreement shall
be, and hereby is, adopted as a plan of reorganization for purposes of Section
368 of the Code;

    NOW, THEREFORE, in consideration of the foregoing and the representations,
warranties, covenants and agreements set forth herein, and other good and
valuable consideration, the receipt and adequacy of which are hereby
acknowledged, and intending to be legally bound hereby, the parties hereto
hereby agree as follows:

                                   ARTICLE I
                                  DEFINITIONS

    SECTION 1.01  Certain Defined Terms

    Unless the context otherwise requires, the following terms, when used in
this Agreement, shall have the respective meanings specified below (such
meanings to be equally applicable to the singular and plural forms of the terms
defined):

    "Affiliate" shall mean, with respect to any person, any other person that
controls, is controlled by or is under common control with the first person.

    "Blue Sky Laws" shall mean state securities or "blue sky" laws.

    "Business day" shall mean any day on which the principal offices of the SEC
in Washington, D.C. are open to accept filings, or, in the case of determining a
date when any payment is due, any day on which banks are not required or
authorized by law or executive order to close in New York.
<PAGE>
    "Company Disclosure Schedule" shall mean the disclosure schedule delivered
by Company to Parent prior to the execution of this Agreement and forming a part
hereof.

    "Company Intellectual Property" shall mean all patents (including, without
limitation, all U.S. and foreign patents, patent applications, patent
disclosures, and any and all divisions, continuations, continuations-in-part,
reissues, re-examinations and extensions thereof), design rights, trademarks,
trade names and service marks (whether or not registered), trade dress, Internet
domain names, copyrights (whether or not registered) and any renewal rights
therefor, sui generis database rights, statistical models, technology,
inventions, supplier lists, trade secrets, know-how, computer software programs
or applications in both source and object code form, databases, technical
documentation of such software programs ("Technical Documentation"),
registrations and applications for any of the foregoing and all other tangible
or intangible proprietary information or materials that were material to
Company's business or are currently used in Company's business in any product,
technology or process (i) currently being or formerly manufactured, published or
marketed by Company or (ii) previously or currently under development for
possible future manufacturing, publication, marketing or other use by Company.

    "Company Material Adverse Effect" shall mean any change in or effect on the
business of Company and the Company Subsidiaries that, individually or in the
aggregate (taking into account all other such changes or effects), is, or is
reasonably likely to be, materially adverse to the business, assets,
liabilities, financial condition or results of operations of Company and the
Company Subsidiaries, taken as a whole, except to the extent that any such
change in or effect results from (i) changes in general economic conditions or
changes affecting the industry generally in which Company operates (provided
that such changes do not affect Company in a materially disproportionate
manner), (ii) changes in trading prices for the Company's capital stock, and
(iii) any litigation or loss of customers or revenues that Company successfully
bears the burden of proving arose from Company entering into this Agreement.

    "Company Stock Plans" shall mean Company's 1999 Stock Incentive Plan,
Amended and Restated 1996 Stock Incentive Plan, and Amended and Restated 1989
Stock Option Plan.

    "Competing Transaction" shall mean any of the following involving Company or
Parent, as the case may be (other than the Merger):

        (i) any merger, consolidation, share exchange, business combination or
    other similar transaction;

        (ii) any sale, lease, exchange, mortgage, pledge, transfer or other
    disposition of 20% or more of the assets of such party and its subsidiaries,
    taken as a whole, in a single transaction or series of transactions;

        (iii) any license, joint venture or other arrangement pursuant to which
    Company provides or permits access to all or a majority of its data (on a
    value basis) to a third party, a primary purpose of which party is targeted
    Internet, Web, e-mail or interactive television advertising;

        (iv) any tender offer or exchange offer for 20% or more of the
    outstanding voting securities of such party or the filing of a registration
    statement under the Securities Act in connection therewith;

        (v) any person having acquired beneficial ownership or the right to
    acquire beneficial ownership of, or any "group" (as such term is defined
    under Section 13(d) of the Exchange Act) having been formed that
    beneficially owns or has the right to acquire beneficial ownership of, 20%
    or more of the outstanding voting securities of such party;

        (vi) any solicitation in opposition to the approval of this Agreement by
    the stockholders of such party; or

        (vii) any public announcement of a proposal, plan or intention to do any
    of the foregoing or any agreement to engage in any of the foregoing.

                                      A-2
<PAGE>
For the purpose of Section 9.05(b)(ii)(B) and Section 9.05(c), each reference to
"20%" shall be deemed to be "30%."

    "Confidentiality Agreements" shall mean the confidentiality agreements, each
dated April 21, 1999, between Parent and Company.

    "$" shall mean United States Dollars.

    "Environmental Law" shall mean any Law and any enforceable judicial or
administrative interpretation thereof, including any judicial or administrative
order, consent decree or judgment, relating to pollution or protection of the
environment or natural resources, including, without limitation, those relating
to the use, handling, transportation, treatment, storage, disposal, release or
discharge of Hazardous Material, as in effect as of the date hereof.

    "Environmental Permit" shall mean any permit, approval, identification
number, license or other authorization required under or issued pursuant to any
applicable Environmental Law.

    "ERISA" shall mean the Employee Retirement Income Security Act of 1974, as
amended.

    "Exchange Act" shall mean the Securities Exchange Act of 1934, as amended,
together with the rules and regulations promulgated thereunder.

    "Expenses" shall mean, with respect to any party hereto, all documented
out-of-pocket expenses (including, without limitation, all fees and expenses of
counsel, accountants, investment bankers, experts and consultants to a party
hereto and its affiliates) incurred by such party or on its behalf in connection
with or related to the authorization, preparation, negotiation, execution and
performance of its obligations pursuant to this Agreement and the consummation
of the Merger, the preparation, printing, filing and mailing of the Registration
Statement and the Joint Proxy Statement, the solicitation of stockholder
approvals, the filing of HSR Act notice, if any, and all other matters related
to the transactions contemplated hereby and the closing of the Merger.

    "Governmental Entity" shall mean any United States Federal, state or local
or any foreign governmental, regulatory or administrative authority, agency or
commission or any court, tribunal or arbitral body.

    "Governmental Order" shall mean any order, writ, judgment, injunction,
decree, stipulation, determination or award entered by or with any Governmental
Entity.

    "Hazardous Material" shall mean (i) any petroleum, petroleum products,
by-products or breakdown products, radioactive materials, asbestos-containing
materials or polychlorinated biphenyls or (ii) any chemical, material or
substance defined or regulated as toxic or hazardous or as a pollutant or
contaminant or waste under any applicable Environmental Law.

    "HSR Act" shall mean the Hart-Scott-Rodino Antitrust Improvements Act of
1976, as amended, together with the rules and regulations promulgated
thereunder.

    "IRS" shall mean the United States Internal Revenue Service.

    "Law" shall mean any Federal, state, foreign or local statute, law,
ordinance, regulation, rule, code, order, judgment, decree, other requirement or
rule of law of the United States or any other jurisdiction, and any other
similar act or law.

    "Parent Disclosure Schedule" shall mean the disclosure schedule delivered by
Parent to Company prior to the execution of this Agreement and forming a part
hereof.

    "Parent Material Adverse Effect" shall mean any change in or effect on the
business of Parent and the Parent Subsidiaries that, individually or in the
aggregate (taking into account all other such changes or effects), is, or is
reasonably likely to be, materially adverse to the business, assets,
liabilities, financial

                                      A-3
<PAGE>
condition or results of operations of Parent and the Parent Subsidiaries, taken
as a whole, except to the extent that any such change in or effect results from
(i) changes in general economic conditions or changes affecting the industry
generally in which Parent operates (provided that such changes do not affect
Parent in a materially disproportionate manner) and (ii) any litigation or loss
of customers or revenues that Parent successfully bears the burden of proving
arose from Parent entering into this Agreement; provided, however, that in no
event shall a decrease in the trading price of Parent Common Stock or litigation
relating thereto be considered a Parent Material Adverse Effect.

    "Parent Stock Plans" shall mean Parent's 1999 Non-Officer Stock Option/Stock
Issuance Plan, 1997 Stock Incentive Plan, as amended, and 1996 Stock Option
Plan.

    "Person" shall mean an individual, corporation, partnership, limited
partnership, limited liability company, limited liability partnership,
syndicate, person (including, without limitation, a "person" as defined in
Section 13(d)(3) of the Exchange Act), trust, association, entity or government
or political subdivision, agency or instrumentality of a government.

    "Securities Act" shall mean the Securities Act of 1933, as amended, together
with the rules and regulations promulgated thereunder.

    "subsidiary" shall mean, with respect to any person, any corporation,
partnership, limited partnership, limited liability company, limited liability
partnership, joint venture or other legal entity of which such person (either
alone or through or together with any other subsidiary of such person) owns,
directly or indirectly, a majority of the stock or other equity interests, the
holders of which are generally entitled to vote for the election of the board of
directors or other governing body of such corporation or other legal entity.

    "Tax" shall mean (i) any and all taxes, fees, levies, duties, tariffs,
imposts and other charges of any kind (together with any and all interest,
penalties, additions to tax and additional amounts imposed with respect thereto)
imposed by any Governmental Entity or taxing authority, including, without
limitation, taxes or other charges on or with respect to income, franchises,
windfall or other profits, gross receipts, property, sales, use, capital stock,
payroll, employment, social security, workers' compensation, unemployment
compensation or net worth; taxes or other charges in the nature of excise,
withholding, ad valorem, stamp, transfer, value-added or gains taxes; license,
registration and documentation fees; and customers' duties, tariffs and similar
charges; (ii) any liability for the payment of any amounts of the type described
in (i) as a result of being a member of an affiliated, combined, consolidated or
unitary group for any taxable period; and (iii) any liability for the payment of
amounts of the type described in (i) or (ii) as a result of being a transferee
of, or a successor in interest to, any Person or as a result of an express or
implied obligation to indemnify any person.

    "Tax Return" shall mean any return, statement or form (including, without
limitation, any estimated tax reports or return, withholding tax reports or
return and information report or return) required to be filed with respect to
any Taxes.

                                   ARTICLE II
                                   THE MERGER

    SECTION 2.01  The Merger

    Upon the terms and subject to the conditions set forth in this Agreement,
and in accordance with the DGCL, at the Effective Time (as defined in Section
2.03), Merger Sub shall be merged with and into Company. As a result of the
Merger, the separate corporate existence of Merger Sub shall cease and Company
shall continue as the surviving corporation of the Merger as a wholly owned
subsidiary of Parent (the "Surviving Corporation").

                                      A-4
<PAGE>
    SECTION 2.02  Closing

    Unless this Agreement shall have been terminated and the Merger herein
contemplated shall have been abandoned pursuant to Section 9.01 and subject to
the satisfaction or waiver of the conditions set forth in Article VIII, the
consummation of the Merger shall take place as promptly as practicable (and in
any event within three business days) after satisfaction or waiver of the
conditions set forth in Article VIII, at a closing (the "Closing") to be held at
the offices of Brobeck, Phleger & Harrison LLP, 1633 Broadway, New York, New
York 10019, unless another date, time or place is agreed to by Parent and
Company.

    SECTION 2.03  Effective Time

    At and after the time of the Closing, the parties shall cause the Merger to
be consummated by filing a certificate of merger (the "Certificate of Merger")
with the Secretary of State of the State of Delaware in such form as required
by, and executed in accordance with the relevant provisions of, the DGCL (the
date and time of such filing, or such later date and time as may be set forth
therein, being the "Effective Time").

    SECTION 2.04  Effect of the Merger

    At the Effective Time, the effect of the Merger shall be as provided in the
applicable provisions of the DGCL. Without limiting the generality of the
foregoing, and subject thereto, at the Effective Time, all the property, rights,
privileges, powers and franchises of Company and Merger Sub shall vest in
Company as the Surviving Corporation, and all debts, liabilities and duties of
Company and Merger Sub shall become the debts, liabilities and duties of Company
as the Surviving Corporation.

    SECTION 2.05  Certificate of Incorporation; Bylaws; Directors and Officers
of Surviving Corporation

    Unless otherwise agreed by Parent and Company before the Effective Time, at
the Effective Time:

        (a) the Certificate of Incorporation and the Bylaws of Merger Sub in
    effect immediately prior to the Effective Time shall be the Certificate of
    Incorporation and the Bylaws of the Surviving Corporation, until thereafter
    amended as provided by Law and such Certificate of Incorporation or Bylaws;
    provided, however, that Article I of the Certificate of Incorporation of the
    Surviving Corporation shall be amended to read as follows: "The name of the
    corporation is Abacus Direct Corporation" and the bylaws shall be amended to
    reflect such name change;

        (b) the officers of Merger Sub immediately prior to the Effective Time
    shall serve in their respective offices of the Surviving Corporation from
    and after the Effective Time, in each case until their successors are
    elected or appointed and qualified or until their resignation or removal;
    and

        (c) the directors of Merger Sub immediately prior to the Effective Time
    shall serve as the directors of the Surviving Corporation from and after the
    Effective Time, in each case until their successors are elected or appointed
    and qualified or until their resignation or removal.

                                  ARTICLE III
               CONVERSION OF SECURITIES; EXCHANGE OF CERTIFICATES

    SECTION 3.01  Conversion of Shares

    At the Effective Time, by virtue of the Merger, and without any action on
the part of Parent, Merger Sub, Company or the holders of any of the following
securities:

        (a) each share of Common Stock, $.001 par value, of Company ("Company
    Common Stock") issued and outstanding immediately before the Effective Time
    (excluding those held in the treasury of Company and those owned by any
    wholly owned subsidiary of Company) and all rights in respect

                                      A-5
<PAGE>
    thereof, shall, forthwith cease to exist and be converted into and become
    exchangeable for 1.05 shares (the "Exchange Ratio") of common stock, $.001
    par value, of Parent ("Parent Common Stock");

        (b) each share of Company Common Stock held in the treasury of Company
    or owned by any wholly owned subsidiary of Company immediately prior to the
    Effective Time shall be canceled and retired and no shares of stock or other
    securities of Parent, the Surviving Corporation or any other corporation
    shall be issuable, and no payment or other consideration shall be made, with
    respect thereto; and

        (c) each issued and outstanding share of capital stock of Merger Sub
    shall be converted into and become one fully paid and nonassessable share of
    common stock of the Surviving Corporation.

    SECTION 3.02  Exchange of Shares Other than Treasury Shares

    (a) Exchange Agent. Prior to the Effective Time, Parent shall enter into an
agreement with a bank or trust company to act as exchange agent for the Merger
(the "Exchange Agent") as may be designated by Parent and such agreement and the
Exchange Agent shall be reasonably acceptable to Company.

    (b) Parent to Provide Common Stock and Cash. Promptly after the Effective
Time, Parent shall make available to the Exchange Agent for the benefit of the
holder of Company Common Stock: (i) Certificates of Parent Common Stock ("Parent
Certificates") representing the number of whole shares of Parent Common Stock
issuable pursuant to Section 3.01(a) in exchange for shares of Company Common
Stock outstanding immediately prior to the Effective Time; (ii) sufficient funds
to permit payment in lieu of fractional shares pursuant to Section 3.04 and
(iii) any dividends or distributions to which holders of shares of Company
Common Stock may be entitled pursuant to Section 3.07.

    (c) Exchange Procedures. The Exchange Agent shall mail to each holder of
record of certificates of Company Common Stock ("Company Certificates"), whose
shares were converted into the right to receive shares of Parent Common Stock
(and cash in lieu of fractional shares pursuant to Section 3.04) promptly after
the Effective Time (and in any event no later than three business days after the
Effective Time): (i) a letter of transmittal (which shall specify that delivery
shall be effected, and risk of loss and title to the Company Certificates shall
pass, only upon receipt of the Company Certificates by the Exchange Agent, and
shall be in such form and have such other provisions as Parent may reasonably
specify); and (ii) instructions for use in effecting the surrender of the
Company Certificates in exchange for Parent Certificates (and cash in lieu of
fractional shares). Upon surrender of a Company Certificate for cancellation to
the Exchange Agent or to such other agent or agents as may be appointed by
Parent, together with such letter of transmittal, duly completed and validly
executed, and such other documents as may be reasonably required by the Exchange
Agent, the holder of such Company Certificate shall be entitled to receive in
exchange therefor a Parent Certificate representing the number of whole shares
of Parent Common Stock that such holder has the right to receive pursuant to
this Article III and payment of cash in lieu of fractional shares which such
holder has the right to receive pursuant to Section 3.04, and the Company
Certificate so surrendered shall forthwith be canceled. Until so surrendered,
each outstanding Company Certificate that, prior to the Effective Time,
represented shares of Company Common Stock will be deemed from and after the
Effective Time, for all corporate purposes other than the payment of dividends
and distributions, to evidence the ownership of the number of full shares of
Parent Common Stock into which such shares of Company Common Stock shall have
been so converted and the right to receive an amount in cash in lieu of the
issuance of any fractional shares in accordance with Section 3.04.
Notwithstanding any other provision of this Agreement, no interest will be paid
or will accrue on any cash payable to holders of Company Certificates pursuant
to the provisions of this Article III.

    (d) Lost, Stolen or Destroyed Company Certificates. In the event any Company
Certificates shall have been lost, stolen or destroyed, the Exchange Agent shall
issue in exchange for such lost, stolen or destroyed Company Certificates, upon
the making of an affidavit of that fact by the holder thereof, a Parent
Certificate representing such shares of Parent Common Stock (and cash in lieu of
fractional shares)

                                      A-6
<PAGE>
as may be required pursuant to this Article III; provided, however, that Parent
may, in its discretion and as a condition precedent to the issuance thereof,
require the owner of such lost, stolen or destroyed Company Certificates to
indemnify Parent against any claim that may be made against Parent, the
Surviving Corporation or the Exchange Agent with respect to the Company
Certificates alleged to have been lost, stolen or destroyed.

    (e) Distributions With Respect to Unexchanged Shares. No dividends or other
distributions with respect to Parent Common Stock with a record date after the
Effective Time will be paid to the holder of any unsurrendered Company
Certificate with respect to the shares of Parent Common Stock represented
thereby until the holder of record of such Company Certificate shall surrender
such Company Certificate. Subject to the effect of applicable escheat or similar
laws, following surrender of any such Company Certificate, there shall be paid
to the record holder of the Parent Certificates issued in exchange therefor,
without interest, at the time of such surrender, the amount of any such
dividends or other distributions with a record date after the Effective Time
theretofore payable (but for the provisions of this Section 3.02(e)) with
respect to such shares of Parent Common Stock.

    (f) Transfer of Ownership. If any Parent Certificate is to be issued in a
name other than that in which the Company Certificate surrendered in exchange
therefor is registered, it will be a condition of the issuance thereof that the
Company Certificate so surrendered will be properly endorsed and otherwise in
proper form for transfer and that the person requesting such exchange will have
paid to Parent or any agent designated by it any transfer or other taxes
required by reason of the issuance of a Parent Certificate for shares of Parent
Common Stock in any name other than that of the registered holder of the Company
Certificate surrendered, or established to the satisfaction of Parent or any
agent designated by it that such tax has been paid or is not payable.

    (g) Termination of Exchange Agent Funding. Any portion of funds (including
any interest earned thereon) or Parent Certificates held by the Exchange Agent
which have not been delivered to holders of Company Certificates pursuant to
this Article III within six months after the Effective Time shall promptly be
paid or delivered, as appropriate, to Parent, and thereafter holders of Company
Certificates who have not theretofore complied with the exchange procedures
outlined in and contemplated by this Section 3.02 shall thereafter look only to
Parent (subject to abandoned property, escheat and similar laws) only as general
creditors thereof for their claim for shares of Parent Common Stock, any cash in
lieu of fractional shares of Parent Common Stock and any dividends or
distributions (with a record date after the Effective Time) with respect to
Parent Common Stock to which they are entitled.

    (h) No Liability. Notwithstanding anything to the contrary in this Section
3.02, none of the Exchange Agent, the Surviving Corporation or any party hereto
shall be liable to any person in respect of any shares of Parent Common Stock or
cash delivered to a public official pursuant to any applicable abandoned
property, escheat or similar law.

    SECTION 3.03  Stock Transfer Books

    (a) At the Effective Time, the stock transfer books of Company shall each be
closed, and there shall be no further registration of transfers of shares of
Company Common Stock thereafter on the records of any such stock transfer books.
In the event of a transfer of ownership of shares of Company Common Stock that
is not registered in the stock transfer records of Company at the Effective
Time, a certificate or certificates representing the number of full shares of
Parent Common Stock into which such shares of Company Common Stock shall have
been converted shall be issued to the transferee together with a cash payment in
lieu of fractional shares, if any, in accordance with Section 3.04 hereof, and a
cash payment in the amount of dividends, if any, in accordance with Section
3.02(e) hereof, if the certificate or certificates representing such shares of
Company Common Stock is or are surrendered as provided in Section
3.02(c) hereof, accompanied by all documents required to evidence and effect
such transfer and by evidence of payment of any applicable stock transfer tax.

                                      A-7
<PAGE>
    (b) Notwithstanding anything to the contrary herein, certificates
surrendered for exchange by any person constituting an affiliate of Company
shall not be exchanged until Parent shall have received from such person an
affiliate letter as provided in Section 7.03.

    SECTION 3.04  No Fractional Share Certificates

    No scrip or fractional share Parent Certificate shall be issued upon the
surrender for exchange of Company Certificates, and an outstanding fractional
share interest shall not entitle the owner thereof to vote, to receive dividends
or to any rights of a stockholder of Parent or of Surviving Corporation with
respect to such fractional share interest. As promptly as practicable following
the Effective Time, Parent shall deposit with the Exchange Agent an amount in
cash sufficient for the Exchange Agent to pay each holder of Company Common
Stock an amount in cash equal to the product obtained by multiplying (i) the
fractional share interest to which such holder would otherwise be entitled
(after taking into account all shares of Company Common Stock held at the
Effective Time by such holder) by (ii) the closing price for a share of Parent
Common Stock on the Nasdaq National Market (the "NNM") on the last business day
prior to the Effective Time. As soon as practicable after the determination of
the amount of cash, if any, to be paid to holders of Company Common Stock with
respect to any fractional share interests, the Exchange Agent shall make
available such amounts, net of any required withholding Taxes, to such holders
of Company Common Stock, subject to and in accordance with the terms of Section
3.02 hereof.

    SECTION 3.05  Options to Purchase Company Common Stock

    At the Effective Time, each option or warrant granted by Company to purchase
shares of Company Common Stock ("Company Stock Options"), which is outstanding
and unexercised immediately prior to the Effective Time, and the Company Stock
Plans shall be assumed by Parent, and the Company Stock Options shall be
converted into an option or warrant, as the case may be, to purchase shares of
Parent Common Stock in such number and at such exercise price as provided below
and otherwise having the same terms and conditions as in effect immediately
prior to the Effective Time (except to the extent that such terms, conditions
and restrictions may be altered in accordance with their terms as a result of
the Merger contemplated hereby and except that all references in each such
Company Stock Option to Company shall be deemed to refer to Parent):

        (a) the number of shares of Parent Common Stock to be subject to the new
    option or warrant, as the case may be, shall be equal to the product of (x)
    the number of shares of Company Common Stock subject to the original Company
    Stock Option immediately prior to the Effective Time and (y) the Exchange
    Ratio;

        (b) the exercise price per share of Parent Common Stock under the new
    option or warrant shall be equal to (x) the exercise price per share of
    Company Common Stock in effect under the original Company Stock Option
    immediately prior to the Effective Time divided by (y) the Exchange Ratio;
    and

        (c) in effecting such assumption and conversion, the aggregate number of
    shares of Parent Common Stock to be subject to each assumed Company Stock
    Option will be rounded down, if necessary, to the next whole share and the
    aggregate exercise price shall be rounded up, if necessary, to the next
    whole cent (for the purpose of providing that the intrinsic value of such
    Company Stock Options shall be preserved at the Effective Time).

    The adjustments provided herein with respect to any options that are
"incentive stock options" (as defined in Section 422 of the Code) shall be
effected in a manner consistent with the requirements of Section 424(a) of the
Code so as to retain their character as incentive stock options. The assumption
of the outstanding Company Stock Options in the Merger and their conversion into
options for Parent Common Stock will not result in any accelerated vesting of
those options or the shares purchasable thereunder other than as contemplated in
presently existing agreements to which the Company is a party, copies of which
agreements have been provided to Parent, and the vesting schedule in effect for
each Company Stock Option immediately prior to the Effective Time shall remain
in full force after the assumption thereof by Parent.

                                      A-8
<PAGE>
    SECTION 3.06  Unvested Stock

    At the Effective Time, any unvested shares of Company Common Stock awarded
to employees, directors or consultants pursuant to any of the Company's plans or
arrangements and outstanding immediately prior to the Effective Time shall be
converted into unvested shares of Parent Common Stock in accordance with the
Exchange Ratio and shall remain subject to the same terms, restrictions and
vesting schedule as in effect immediately prior to the Effective Time, except to
the extent by their terms such unvested shares of Company Common Stock vest at
the Effective Time and copies of the relevant agreements governing such vesting
have been provided to Parent. All outstanding rights which Company may hold
immediately prior to the Effective Time to repurchase unvested shares of Company
Common Stock shall be assigned to the Parent in the Merger and shall thereafter
be exercisable by Parent upon the same terms and conditions in effect
immediately prior to the Effective Time, except that the shares purchasable
pursuant to such rights and the purchase price payable per share shall be
adjusted to reflect the Exchange Ratio.

    SECTION 3.07  Certain Adjustments

    If between the date of this Agreement and the Effective Time, the
outstanding shares of Parent Common Stock or Company Common Stock shall be
changed into a different number of shares by reason of any reclassification,
recapitalization, split-up, combination or exchange of shares, or any dividend
payable in stock or other securities shall be declared thereon with a record
date within such period, or the number of shares of Company Common Stock on a
fully diluted basis is in excess of that specified in Section 4.03 and disclosed
in Section 4.03 of the Company Disclosure Schedule (regardless of whether such
excess is a result of an additional issuance of capital stock or a correction to
such Sections), then the Exchange Ratio established pursuant to the provisions
of Section 3.01 shall be adjusted accordingly to provide to each of Parent, on
the one hand, and the holders of Company Common Stock in the aggregate, on the
other hand, the same economic effect as contemplated by this Agreement prior to
such reclassification, recapitalization, split-up, combination, exchange,
dividend or increase.

                                   ARTICLE IV
                   REPRESENTATIONS AND WARRANTIES OF COMPANY

    Company hereby represents and warrants to Parent, subject to the exceptions
specifically disclosed in writing in the Company Disclosure Schedule, all such
exceptions to be referenced to a specific representation set forth in this
Article IV or to otherwise be clearly applicable to representations hereof not
specifically referenced, that:

    SECTION 4.01  Organization and Qualification; Subsidiaries

    (a) Company and each directly and indirectly owned subsidiary of Company
(the "Company Subsidiaries") has been duly organized and is validly existing and
in good standing (to the extent applicable) under the laws of the jurisdiction
of its incorporation or organization, as the case may be, and has the requisite
corporate power and authority to own, lease and operate its properties and to
carry on its business as it is now being conducted. Company and each Company
Subsidiary is duly qualified or licensed to do business, and is in good standing
(to the extent applicable), in each jurisdiction where the character of the
properties owned, leased or operated by it or the nature of its business makes
such qualification or licensing necessary.

    (b) Section 4.01 of the Company Disclosure Schedule sets forth, as of the
date of this Agreement, a true and complete list of each Company Subsidiary,
together with (i) the jurisdiction of incorporation or organization of each
Company Subsidiary and the percentage of each Company Subsidiary's outstanding
capital stock or other equity interests owned by Company or another Company
Subsidiary and (ii) an indication of whether each Company Subsidiary is a
"Significant Subsidiary" as defined in Regulation S-X

                                      A-9
<PAGE>
under the Exchange Act. Except as set forth in Section 4.01 of the Company
Disclosure Schedule, neither Company nor any Company Subsidiary owns an equity
interest in any partnership or joint venture arrangement or other business
entity.

    SECTION 4.02  Certificate of Incorporation and Bylaws

    The copies of Company's certificate of incorporation and bylaws previously
provided to Parent by Company are true, complete and correct copies thereof.
Such certificate of incorporation and bylaws are in full force and effect.
Company is not in violation of any of the provisions of its certificate of
incorporation or bylaws.

    SECTION 4.03  Capitalization

    The authorized capital stock of Company consists of 25,000,000 shares of
Company Common Stock and 1,000,000 shares of preferred stock ("Company Preferred
Stock"). As of the date hereof, (i) 9,877,521 shares of Company Common Stock are
issued and outstanding, all of which are validly issued, fully paid and
nonassessable, (ii) no shares of Company Common Stock are held in the treasury
of Company, (iii) no shares of Company Common Stock are held by Company
Subsidiaries, (iv) 2,151,298 shares of Company Common Stock are reserved for
future issuance pursuant to Company Stock Options, of which 1,820,523 and
330,775 shares of Company Common Stock are reserved for future issuance pursuant
to unvested, outstanding and vested, outstanding, unexercised Company Stock
Options, respectively, and (v) no shares of Company Preferred Stock are
outstanding. The name of each holder of a Company Stock Option, the grant date
of each Company Stock Option, and the number of shares of Company Common Stock
for which each Company Stock Option is exercisable and the exercise price of
each Company Stock Option are set forth in Section 4.03 of the Company
Disclosure Schedule. Except for shares of Company Common Stock issuable pursuant
to Company Stock Plans, there are no options, warrants or other rights,
agreements, arrangements or commitments of any character obligating Company or
any Company Subsidiary to issue or sell any shares of capital stock of, or other
equity interests in, Company or any Company Subsidiary. All shares of Company
Common Stock subject to issuance as aforesaid, upon issuance prior to the
Effective Time on the terms and conditions specified in the instruments pursuant
to which they are issuable, will be duly authorized, validly issued, fully paid
and nonassessable. There are no outstanding contractual obligations of Company
or any Company Subsidiary to repurchase, redeem or otherwise acquire any shares
of Company Common Stock or any capital stock of any Company Subsidiary. Each
outstanding share of capital stock of each Company Subsidiary is duly
authorized, validly issued, fully paid and nonassessable and each such share
owned by Company or another Company Subsidiary is free and clear of all security
interests, liens, claims, pledges, options, rights of first refusal, agreements,
limitations on Company's or such other Company Subsidiary's voting rights,
charges and other encumbrances of any nature whatsoever. There are no material
outstanding contractual obligations of Company or any Company Subsidiary to
provide funds to, or make any material investment (in the form of a loan,
capital contribution or otherwise) in, any Company Subsidiary or any other
person.

    SECTION 4.04  Authority Relative to This Agreement

    Company has all necessary corporate power and authority to execute and
deliver this Agreement and the Option Agreement, to perform its obligations
hereunder and thereunder and to consummate the transactions contemplated hereby
and thereby. The execution and delivery of this Agreement and the Option
Agreement by Company and the consummation by Company of the transactions
contemplated hereby and thereby have been duly and validly authorized by all
necessary corporate action, and no other corporate proceedings on the part of
Company are necessary to authorize this Agreement and the Option Agreement or to
consummate the transactions contemplated hereby and thereby (other than, with
respect to the Merger, the approval of this Agreement by the holders of a
majority of the outstanding shares of Company Common Stock entitled to vote with
respect thereto at the Company Stockholders' Meeting (as defined in Section
7.01), and the filing and recordation of the Certificate of Merger as required
by the DGCL). This Agreement and the Option Agreement have been duly executed
and delivered by Company

                                      A-10
<PAGE>
and, assuming the due authorization, execution and delivery by the other parties
hereto and thereto, constitute legal, valid and binding obligations of Company,
enforceable against Company in accordance with their terms, subject to the
effect of any applicable bankruptcy, moratorium, insolvency, reorganization or
other similar law affecting the enforceability of creditors' rights generally
and to the effect of general principles of equity which may limit the
availability of remedies (whether in a proceeding at law or in equity).

    SECTION 4.05  No Conflict; Required Filings and Consents

    (a) The execution and delivery of this Agreement and the Option Agreement by
Company do not, and the performance by Company of its obligations hereunder and
thereunder and the consummation of the Merger will not, (i) conflict with or
violate any provision of the certificate of incorporation or bylaws of Company
or any equivalent organizational documents of any Company Subsidiary,
(ii) assuming that all filings and notifications described in Section
4.05(b) have been made, conflict with or violate any Law applicable to Company
or any Company Subsidiary or by which any property or asset of Company or any
Company Subsidiary is bound or affected or (iii) result in any material breach
of or constitute a material default (or an event which with the giving of notice
or lapse of time or both could reasonably be expected to become a default)
under, or give to others any right of termination, amendment, acceleration or
cancellation of, or result in the creation of a lien or other encumbrance on any
material property or asset of Company or any Company Subsidiary pursuant to, any
material note, bond, mortgage, indenture, contract, agreement, lease, license,
permit, franchise or other instrument or obligation.

    (b) Except as may arise solely by virtue of the nature of Parent's business,
the execution and delivery of this Agreement by Company do not, and the
performance by Company of its obligations hereunder and the consummation of the
Merger will not, require any consent, approval, authorization or permit of, or
filing by Company with or notification by Company to, any Governmental Entity,
except pursuant to applicable requirements of the Exchange Act, the Securities
Act, Blue Sky Laws, the rules and regulations of the NNM, state takeover laws,
the premerger notification requirements of the HSR Act, and the filing and
recordation of the Certificate of Merger as required by the DGCL.

    SECTION 4.06  Permits; Compliance with Laws

    Company and the Company Subsidiaries are in possession of all franchises,
grants, authorizations, licenses, establishment registrations, product listings,
permits, easements, variances, exceptions, consents, certificates,
identification and registration numbers, approvals and orders of any
Governmental Entity materially necessary for Company or any Company Subsidiary
to own, lease and operate its properties or to offer or perform its services or
to develop, produce, store, distribute and market its products or otherwise to
carry on its business as it is now being conducted (collectively, the "Company
Permits"), and, as of the date of this Agreement, none of the Company Permits
has been suspended or cancelled nor is any such suspension or cancellation
pending or, to the knowledge of Company, threatened. Neither Company nor any
Company Subsidiary is in conflict with, or in default or violation of, (i) any
Law applicable to Company or any Company Subsidiary or by which any property or
asset of Company or any Company Subsidiary is bound or affected or (ii) any
material Company Permits. Section 4.06 of the Company Disclosure Schedule sets
forth, as of the date of this Agreement, all actions, proceedings,
investigations or surveys pending or, to the knowledge of Company, threatened
against Company or any Company Subsidiary that could reasonably be expected to
result in the suspension or cancellation of any other material Company Permit.
Since January 1, 1997, neither Company nor any Company Subsidiary has received
from any Governmental Entity any written notification with respect to possible
material conflicts, defaults or violations of Laws.

    SECTION 4.07  SEC Filings; Financial Statements

    (a) Company has timely filed all forms, reports, statements and documents
required to be filed by it (A) with the SEC and the NNM since November 1, 1996
(collectively, together with any such forms,

                                      A-11
<PAGE>
reports, statements and documents Company may file subsequent to the date hereof
until the Closing, the "Company Reports") and (B) with any other Governmental
Entities. Each Company Report (i) was prepared in accordance with the
requirements of the Securities Act, the Exchange Act or the rules and
regulations of the NNM, as the case may be, in substantially all respects and
(ii) did not at the time it was filed contain any untrue statement of a material
fact or omit to state a material fact required to be stated therein or necessary
in order to make the statements made therein, in the light of the circumstances
under which they were made, not misleading. Each form, report, statement and
document referred to in clause (B) of this paragraph was prepared in all
material respects in accordance with the requirements of applicable Law. No
Company Subsidiary is subject to the periodic reporting requirements of the
Exchange Act or required to file any form, report or other document with the
SEC, the NNM, any other stock exchange or any other comparable Governmental
Entity.

    (b) Each of the consolidated financial statements (including, in each case,
any notes thereto) contained in the Company Reports was prepared in accordance
with U.S. GAAP (except as may be permitted by Form 10-Q under the Exchange Act)
applied on a consistent basis throughout the periods indicated (except as may be
indicated in the notes thereto) and each presented fairly, in all material
respects, the consolidated financial position of Company and the consolidated
Company Subsidiaries as at the respective dates thereof and for the respective
periods indicated therein, except as otherwise noted therein (subject, in the
case of unaudited statements, to normal and recurring immaterial year-end
adjustments).

    (c) Except as and to the extent set forth or reserved against on the
consolidated balance sheet of Company and the Company Subsidiaries as reported
in the Company Reports, including the notes thereto, none of Company or any
Company Subsidiary has any liabilities or obligations of any nature (whether
accrued, absolute, contingent or otherwise) that would be required to be
reflected on a balance sheet or in notes thereto prepared in accordance with
U.S. GAAP, except for immaterial liabilities or obligations incurred in the
ordinary course of business consistent with past practice since December 31,
1998.

    SECTION 4.08  Absence of Certain Changes or Events

    Since December 31, 1998, Company and the Company Subsidiaries have conducted
their businesses in all material respects only in the ordinary course consistent
with past practice and, since such date, there has not been (i) any material
changes in or effect on the business, assets, liabilities, financial condition
or results of operations of Company or the Company Subsidiaries, (ii) any event
(other than events within the scope of Section 4.10) that could reasonably be
expected to prevent or materially delay the performance of Company's obligations
pursuant to this Agreement and the consummation of the Merger by Company,
(iii) any material change by Company in its accounting methods, principles or
practices, (iv) any declaration, setting aside or payment of any dividend or
distribution in respect of the shares of Company Common Stock or any redemption,
purchase or other acquisition of any of Company's securities, (v) except for
changes in the ordinary course of business consistent with past practice that
only affect non-officer employees of the Company, any increase in the
compensation or benefits or establishment of any bonus, insurance, severance,
deferred compensation, pension, retirement, profit sharing, stock option
(including, without limitation, the granting of stock options, stock
appreciation rights, performance awards or restricted stock awards), stock
purchase or other employee benefit plan, or any other increase in the
compensation payable or to become payable to any employees, officers,
consultants or directors of Company or any Company Subsidiary, (vi) any issuance
or sale of any stock, notes, bonds or other securities other than pursuant to
the exercise of outstanding securities, or entering into any agreement with
respect thereto, or the issuances of options under the Company Stock Plans,
(vii) any amendment to the Company's certificate of incorporation or bylaws,
(viii) other than in the ordinary course of business consistent with past
practice, any (x) purchase, sale, assignment or transfer of any material assets,
(y) mortgage, pledge or existence of any lien, encumbrance or charge on any
material assets or properties, tangible or intangible except for liens for Taxes
not yet delinquent, or (z) waiver of any rights of material value or
cancellation or any material debts or claims, (ix) any incurrence of any
material liability (absolute

                                      A-12
<PAGE>
or contingent), except for current liabilities and obligations incurred in the
ordinary course of business consistent with past practice, (x) any incurrence of
any damage, destruction or similar loss, whether or not covered by insurance,
materially affecting the business or properties of Company or any Company
Subsidiary, or (xi) any entering into any transaction of a material nature other
than in the ordinary course of business, consistent with past practice.

    SECTION 4.09  Employee Benefit Plans; Labor Matters

    (a) The Company Disclosure Schedule lists each employee benefit fund, plan,
program, arrangement and contract (including, without limitation, any "pension"
plan, fund or program, as defined in Section 3(2) of ERISA, and any "employee
benefit plan", as defined in Section 3(3) of ERISA and any plan, program,
arrangement or contract providing for severance; medical, dental or vision
benefits; life insurance or death benefits; disability benefits, sick pay or
other wage replacement; vacation, holiday or sabbatical; pension or
profit-sharing benefits; stock options or other equity compensation; bonus or
incentive pay or other material fringe benefits) ("Benefit Plans"), maintained,
sponsored or contributed to or required to be contributed to by Company or any
Company Subsidiary (the "Company Benefit Plans"). With respect to each Company
Benefit Plan, Company has delivered or made available to Parent a true, complete
and correct copy of (i) such Company Benefit Plan (of, if not written, a written
summary of its material terms) and the most recent summary plan description, if
any, related to such Company Benefit Plan, (ii) each trust agreement or other
funding arrangement relating to such Company Benefit Plan, (iii) the most recent
annual report (Form 5500) filed with the IRS with respect to such Company
Benefit Plan (and, if the most recent annual report is a Form 5500R, the most
recent Form 5500C filed with respect to such Company Benefit Plan), (iv) the
most recent actuarial report or financial statement relating to such Company
Benefit Plan and (v) the most recent determination letter, if any, issued by the
IRS with respect to such Company Benefit Plan and any pending request for such a
determination letter. Neither Company nor any Company Subsidiary nor, to the
knowledge of Company, any other person or entity, has any express commitment,
whether legally enforceable or not, to modify, change or terminate any Company
Benefit Plan, other than with respect to a modification, change or termination
required by ERISA or the Code.

    (b) Each Company Benefit Plan has been administered in all material respects
in accordance with its terms and all applicable laws, including ERISA and the
Code, and contributions required to be made under the terms of any of the
Company Benefit Plans as of the date of this Agreement have been timely made or,
if not yet due, have been properly reflected on the most recent consolidated
balance sheet filed or incorporated by reference in the Company Reports prior to
the date of this Agreement. With respect to the Company Benefit Plans, to
Company's knowledge, no event has occurred and, to the knowledge of Company,
there exists no condition or set of circumstances in connection with which
Company or any Company Subsidiary could be subject to any material liability
(other than for routine benefit liabilities) under the terms of, or with respect
to, such Company Benefit Plans, ERISA, the Code or any other applicable Law.

    (c) Company on behalf of itself and each Company ERISA Affiliate (as defined
below) hereby represents that: (i) each Company Benefit Plan which is intended
to qualify under Section 401(a), Section 401(k), Section 401(m) or Section
4975(e)(6) of the Code has received a favorable determination letter from the
IRS as to its qualified status, and each trust established in connection with
any Company which is intended to be exempt from federal income taxation under
Section 501(a) of the Code has received an opinion letter from the IRS that it
is so exempt or application for same is pending that is timely filed with the
IRS, and to Company's knowledge no fact or event has occurred that is reasonably
likely to materially adversely affect the qualified status of any such Company
Benefit Plan or the exempt status of any such trust; (ii) to Company's
reasonable knowledge there has been no prohibited transaction (within the
meaning of Section 406 of ERISA or Section 4975 of the Code and other than a
transaction that is exempt under a statutory or administrative exemption) with
respect to any Company Plan that could result in liability to the Company or a
Company Subsidiary and (iii) each Company Benefit Plan can be amended,

                                      A-13
<PAGE>
terminated or otherwise discontinued after the Effective Time in accordance with
its terms, without liability (other than (A) liability for ordinary
administrative expenses typically incurred in a termination event or (B) if the
Company Benefit Plan is pension benefit plan subject to Part 2 of Title I of
ERISA, liability for the accrued benefits as of the date of such termination (if
and to the extent required by ERISA)) to the extent that either there are
sufficient assets set aside in a trust or insurance contract to satisfy such
liability or such liability is reflected on the most recent consolidated balance
sheet filed or incorporated by reference in the Company Reports prior to the
date of this Agreement. No suit, administrative proceeding, action or other
litigation has been brought, or to the knowledge of Company is threatened,
against or with respect to any such Company Benefit Plan, including any audit or
inquiry by the Internal Revenue Service or United States Department of Labor
(other than routine benefits claims).

    (d) No Company Benefit Plan is a multiemployer pension plan (as defined in
Section 3(37) of ERISA) or other pension plan subject to Title IV of ERISA and
neither the Company, any Company Subsidiary nor any other trade or business
(whether or not incorporated) that is under "common control" with Company or a
Company Subsidiary (within the meaning of ERISA Section 4001) or with respect to
which Company or any Company Subsidiary could otherwise incur liability under
Title IV of ERISA (a "Company ERISA Affiliate") has sponsored or contributed to
or been required to contribute to a multiemployer pension plan or other pension
plan subject to Title IV of ERISA. No material liability under Title IV of ERISA
has been incurred by Company, any Company Subsidiary or any Company ERISA
Affiliate that has not been satisfied in full, and no condition exists that
presents a material risk to Company or any Company Subsidiary of incurring or
being subject (whether primarily, jointly or secondarily) to a material
liability thereunder. None of the assets of Company or any Company Subsidiary
is, or may reasonably be expected to become, the subject of any lien arising
under ERISA or Section 412(n) of the Code.

    (e) With respect to each Benefit Plan required to be set forth in the
Disclosure Schedule that is subject to Title IV or Part 3 of Title I of ERISA or
Section 412 of the Code, (i) no reportable event (within the meaning of Section
4043 of ERISA, other than an event that is not required to be reported before or
within 30 days of such event) has occurred or is expected to occur, (ii) there
was not an accumulated funding deficiency (within the meaning of Section 302 of
ERISA or Section 412 of the Code), whether or not waived, as of the most
recently ended plan year of such Benefit Plan; and (iii) there is no "unfunded
benefit liability" (within the meaning of Section 4001(a)(18) of ERISA).

    (f) Company has made available to Parent true, complete and correct copies
of (i) all employment agreements with officers and all consulting agreements of
Company and each Company Subsidiary, (ii) all severance plans, agreements,
programs and policies of Company and each Company Subsidiary with or relating to
their respective employees, directors or consultants, and (iii) all plans,
programs, agreements and other arrangements of Company and each Company
Subsidiary with or relating to their respective employees, directors or
consultants which contain "change of control" provisions. No payment or benefit
which may be required to be made by Company or any Company Subsidiary or which
otherwise may be required to be made under the terms of any Company Benefit Plan
or other arrangement will constitute a parachute payment under Code Section
280(G)(1), and the consummation of the transactions contemplated by this
Agreement will not, alone or in conjunction with any other possible event
(including termination of employment), (i) entitle any current or former
employee or other service provider of Company or any Company Subsidiary to
severance benefits or any other payment, compensation or benefit (including
forgiveness of indebtedness), except as expressly provided by this Agreement, or
(ii) accelerate the time of payment or vesting, or increase the amount of
compensation or benefit due any such employee or service provider.

    (g) Neither Company nor any Company Subsidiary is a party to, or has any
obligations under or with respect to, any collective bargaining or other labor
union contract applicable to persons employed by Company or any Company
Subsidiary and no collective bargaining agreement is being negotiated by Company
or any Company Subsidiary or any person or entity that may obligate the Company
or any

                                      A-14
<PAGE>
Company Subsidiary thereunder. As of the date of this Agreement, there is no
labor dispute, strike, union organizing activity or work stoppage against
Company or any Company Subsidiary pending or, to the knowledge of Company,
threatened which may substantially interfere with the respective business
activities of Company or any Company Subsidiary. As of the date of this
Agreement, to the knowledge of Company, none of Company, any Company Subsidiary,
or any of their respective representatives or employees has committed any unfair
labor practice in connection with the operation of the respective businesses of
Company or any Company Subsidiary, and there is no charge or complaint filed
against Company or any Company Subsidiary by or with the National Labor
Relations Board or any comparable Governmental Entity pending or threatened in
writing.

    (h) Except as required by Law, no Company Benefit Plan provides any of the
following retiree or post-employment benefits to any person: medical, disability
or life insurance benefits. To Company's knowledge, Company and the Company
ERISA Affiliates are in compliance with (i) the requirements of the applicable
health care continuation and notice provisions of the Consolidated Omnibus
Budget Reconciliation Act of 1985, as amended ("COBRA") and the regulations
(including proposed regulations) thereunder and (ii) the applicable requirements
of the Health Insurance Portability and Accountability Act of 1996, as amended,
and the regulations (including the proposed regulations) thereunder.

    SECTION 4.10  Pooling; Certain Tax Matters

    To Company's knowledge, neither Company nor any of its affiliates has taken
or agreed to take any action (other than actions contemplated by this Agreement)
that could be expected (based on the advice of PricewaterhouseCoopers) to
prevent the Merger from being treated for accounting purposes as a "pooling of
interests" in accordance with U.S. GAAP and the accounting standards of the SEC.
Neither Company, nor to Company's knowledge, any of its affiliates, has taken or
agreed to take any action (other than actions contemplated by this Agreement)
that could be expected to prevent the Merger from constituting a
"reorganization" under Section 368 of the Code. Company is not aware of any
agreement or plan to which Company or any of its affiliates is a party or other
circumstances relating to Company or any of its affiliates that could reasonably
be expected to prevent the Merger from being so treated as a "pooling of
interests" or from so qualifying as a reorganization under Section 368 of the
Code.

    SECTION 4.11  Contracts

    Section 4.11 of the Company Disclosure Schedule sets forth a list of each
contract or agreement that is material to the business, assets, liabilities,
financial condition or results of operations of Company and Company
Subsidiaries, taken as a whole (each, a "Material Contract"). Neither Company
nor any Company Subsidiary is in material violation of or in default under (nor
does there exist any condition which with the passage of time or the giving of
notice could reasonably be expected to cause such a material violation of or
material default under) any Material Contract. Each Material Contract is in full
force and effect and is a legal, valid and binding obligation of Company or a
Company Subsidiary and, to the knowledge of Company, each of the other parties
thereto, enforceable in accordance with its terms.

    SECTION 4.12  Litigation

    There is no material suit, claim, action, proceeding or investigation
pending or, to the knowledge of Company, threatened against Company or any
Company Subsidiary, and, to the knowledge of Company, there are no existing
facts or circumstances that could reasonably be expected to result in such a
suit, claim, action, proceeding or investigation. Company is not aware of any
facts or circumstances which could reasonably be expected to result in the
denial of insurance coverage under policies issued to Company and Company
Subsidiaries in respect of such material suits, claims, actions, proceedings and
investigations. Neither Company nor any Company Subsidiary is subject to any
material outstanding order, writ, injunction or decree or any material
outstanding order, writ, injunction or decree.

                                      A-15
<PAGE>
    SECTION 4.13  Environmental Matters

    To Company's knowledge, (i) Company and the Company Subsidiaries are in
material compliance with all applicable Environmental Laws and all Company
Permits required by Environmental Laws; (ii) all past noncompliance of Company
or any Company Subsidiary with Environmental Laws or Environmental Permits has
been resolved without any pending, ongoing or future material obligation, cost
or liability; and (iii) neither Company nor any Company Subsidiary has released
a Hazardous Material at, or transported a Hazardous Material to or from, any
real property currently or formerly owned, leased or occupied by Company or any
Company Subsidiary, in violation of any Environmental Law.

    SECTION 4.14  Intellectual Property

    (a) Section 4.14(a) of the Company Disclosure Schedule contains a true and
complete list of Company's patents, patent applications, registered trademarks,
trademark applications, trade names, registered service marks, service mark
applications, Internet domain names, Internet domain name applications,
copyright registrations and applications and other filings and formal actions
made or taken pursuant to Federal, state, local and foreign laws by Company to
protect its interests in Company Intellectual Property, and includes details of
all due dates for further filings, maintenance, payments or other actions
falling due in respect of Company Intellectual Property within twelve (12)
months of the Effective Time. All of Company's patents, patent applications,
registered trademarks, and trademark applications, and registered copyrights
remain in good standing with all fees and filings due as of the date hereof. The
Company has previously provided Purchaser with a list of all other trademarks
and service marks which are material to the Company's business.

    (b) Company has made all registrations that Company (including any of its
subsidiaries) is required to have made in relation to the processing of data,
and is in good standing with respect to such registrations with all fees due as
of the Effective Time duly made.

    (c) Company Intellectual Property contains only those items and rights which
are: (i) owned by Company; (ii) in the public domain; or (iii) rightfully used
by Company pursuant to a valid and enforceable license or other agreement (the
"Company Licensed Intellectual Property"), the parties, date, term and subject
matter of each such license or other agreement (each, a "License Agreement")
being set forth on Section 4.14(c) of the Company Disclosure Schedule. Company
has all rights in Company Intellectual Property necessary to carry out Company's
current activities and, to the knowledge of the Company, the Company's future
activities to the extent such future activities are already planned, including
without limitation, to the extent required to carry out such activities, rights
to make, use, reproduce, modify, adopt, create derivative works based on,
translate, distribute (directly and indirectly), transmit, display and perform
publicly, license, rent and lease and, other than with respect to Company
Licensed Intellectual Property, assign and sell, Company Intellectual Property.

    (d) The reproduction, manufacturing, distribution, licensing, sublicensing,
sale or any other exercise of rights in any Company Intellectual Property,
product, work, technology or process as now used or offered or proposed for use,
licensing or sale by Company does not infringe on any patent, design right,
trademark, trade name, service mark, trade dress, Internet domain name,
copyright, database, statistical model, technology, invention, supplier list,
trade secret, know-how, computer software program or application of any person,
anywhere in the World. The Company has not received notice of any claims
(i) challenging the validity, effectiveness or, other than with respect to
Company Licensed Intellectual Property, ownership by Company of any Company
Intellectual Property, or (ii) to the effect that the use, distribution,
licensing, sublicensing, sale or any other exercise of rights in any product,
work, technology or process as now used or offered or proposed for use,
licensing, sublicensing or sale by Company or its agents or use by its customers
infringes or will infringe on any intellectual property or other proprietary or
personal right of any person. To the knowledge of Company, no such claims have
been threatened by any person, nor are there any valid grounds for any bona fide
claim of any such kind. All of the rights within Company Intellectual Property
are enforceable and subsisting. To the knowledge of Company, there is no

                                      A-16
<PAGE>
unauthorized use, infringement or misappropriation of any Company Intellectual
Property by any third party, employee or former employee.

    (e) All personnel, including employees, agents, consultants and contractors,
who have contributed to or participated in the conception and development of
Company Intellectual Property on behalf of Company, have executed nondisclosure
agreements and either (i) have been a party to an enforceable "work-for-hire"
arrangement or agreements with Company in accordance with applicable national
and state law that has accorded Company full, effective, exclusive and original
ownership of all tangible and intangible property thereby arising, or (ii) have
executed appropriate instruments of assignment in favor of Company as assignee
that have conveyed to Company effective and exclusive ownership of all tangible
and intangible property thereby arising.

    (f) Company is not, nor as a result of the execution or delivery of this
Agreement, or performance of Company's obligations hereunder, will Company be,
in violation of any material license, sublicense, agreement or instrument to
which Company is a party or otherwise bound, nor will execution or delivery of
this Agreement, or performance of Company's obligations hereunder, cause the
diminution, termination or forfeiture of any Company Intellectual Property.

    (g) Section 4.14(g) of the Company Disclosure Schedule contains a true and
complete list of all software programs which are owned by the Company (the
"Company Software Programs"). Company owns full and unencumbered right and good,
valid and marketable title to such the Company Software Programs free and clear
of all mortgages, pledges, liens, security interests, conditional sales
agreements, encumbrances or charges of any kind.

    (h) The source code and system documentation relating to the Company
Software Programs have been maintained in strict confidence and (i) have been
disclosed by Company only to those of its employees who have a "need to know"
the contents thereof in connection with the performance of their duties to
Company and who have executed nondisclosure agreements with Company; and (ii)
have been disclosed to only those third parties who have executed nondisclosure
agreements with Company.

    (i) Company has taken all reasonable steps, in accordance with normal
industry practice, to preserve and maintain complete notes and records relating
to Company Intellectual Property to cause the same to be readily identified and
available.

    (j) Section 4.14(j) of the Company Disclosure Schedule sets forth a
description, and the current status, of Company's Year 2000 compliance program
and its anticipated completion date. Upon completion of the Company's Year 2000
compliance program, the Company Software Programs shall (i) have been designed
to ensure year 2000 compatibility, which includes, but is not limited to, date
data century recognition, and calculations that accommodate same century and
multi-century formulas and date values; (ii) operate in accordance with their
specifications prior to, during and after the calendar year 2000 AD; and (iii)
not end abnormally or provide invalid or incorrect results as a result of date
data, specifically including date data which represents or references different
centuries or more than one century.

    (k) Company Intellectual Property is free and clear of any and all
mortgages, pledges, liens, security interests, conditional sale agreements,
encumbrances or charges of any kind.

    (l) Except as set forth in the Company Disclosure Schedule, Company
(including its subsidiaries) does not owe any royalties or other payments to
third parties in respect of Company Intellectual Property. All royalties or
other payments set forth in the Company Disclosure Schedule that have accrued
prior to the Effective Time have been paid.

    (m) Company's (including its subsidiaries) statistical models have not been
disclosed to any third party at any time other than to third parties who have
executed nondisclosure agreements with Company.

                                      A-17
<PAGE>
    (n) To the knowledge of the Company and other than as disclosed on the
Company Disclosure Schedule, all Company "Alliance members" are in compliance
with the terms of their respective agreement with Company.

    (o) It is the Company's practice to scan the Company Intellectual Property
with a commercially available virus scan software. To the Company's knowledge,
the Company Software Programs and other Company Intellectual Property contain no
"viruses." For the purposes of this Agreement, "virus" means any computer code
intentionally designed to disrupt, disable or harm in any manner the operation
of any software or hardware. None of the foregoing contains any worm, bomb,
backdoor, clock, timer, or other disabling device code, design or routine which
causes the software to be erased, inoperable, or otherwise incapable of being
used, either automatically or upon command by any party.

    (p) Company has implemented all reasonable steps which are known in the
information systems industry and which are generally known as best practices in
the physical and electronic protection of its information assets from
unauthorized disclosure, use or modification. Company has previously disclosed
to Parent whether, to its knowledge, there have been breaches of security, known
consequences, and the steps Company has taken to remedy any such breaches.

    (q) Company has conducted its business and has collected, maintained and
used its data at all times materially in accordance with (i) accepted industry
practice and the standards promulgated by the Direct Marketing Association; and
(ii) all applicable Laws, including but not limited to those affecting privacy
issues.

    SECTION 4.15  Taxes

    (a) Company and each of Company Subsidiaries, and any consolidated,
combined, unitary or aggregate group for Tax purposes of which Company or any
Company Subsidiary is or has been a member, have properly completed and timely
filed all Tax Returns required to be filed by them and have paid all Taxes shown
thereon to be due. Company has provided adequate accruals in accordance with
generally accepted accounting principles in its latest financial statements
included in the Company Reports for any Taxes that have not been paid, whether
or not shown as being due on any Tax Returns. Company and the Company
Subsidiaries have no material liability for unpaid Taxes accruing after the date
of the Company's latest financial statements included in the Company Reports.

    (b) There is (i) no material claim for Taxes that is a lien against the
property of Company or any Company Subsidiary or is being asserted against
Company or any Company Subsidiary other than liens for Taxes not yet due and
payable, (ii) no audit of any Tax Return of Company or any Company Subsidiary
being conducted by a Tax Authority; (iii) no extension of the statute of
limitations on the assessment of any Taxes granted by Company or any Company
Subsidiary and currently in effect, and (iv) no agreement, contract or
arrangement to which Company or any Company Subsidiary is a party that may
result in the payment of any amount that would not be deductible by reason of
Section 280G or Section 404 of the Code.

    (c) There has been no change in ownership of Company or any Company
Subsidiaries that has caused the utilization of any losses of such entities to
be limited pursuant to Section 382 of the Code, and any loss carryovers
reflected on the latest financial statements included in the Company Reports are
properly computed and reflected.

    (d) Company and the Company Subsidiaries have not been and will not be
required to include any material adjustment in Taxable income for any Tax period
(or portion thereof) pursuant to Section 481 or 263A of the Code or any
comparable provision under state or foreign Tax laws as a result of
transactions, events or accounting methods employed prior to the Merger.

                                      A-18
<PAGE>
    (e) Neither Company nor any Company Subsidiary has filed or will file any
consent to have the provisions of paragraph 341(f)(2) of the Code (or comparable
provisions of any state Tax laws) apply to Company or any Company Subsidiary.

    (f) Neither Company nor any Company Subsidiary is a party to any Tax sharing
or Tax allocation agreement nor does Company or any Company Subsidiary have any
liability or potential liability to another party under any such agreement.

    (g) Neither Company nor any Company Subsidiary has filed any disclosures
under Section 6662 or comparable provisions of state, local or foreign law to
prevent the imposition of penalties with respect to any Tax reporting position
taken on any Tax Return.

    (h) Neither Company nor any Company Subsidiary has ever been a member of a
consolidated, combined or unitary group of which Company was not the ultimate
parent corporation.

    (i) Company and each Company Subsidiary has in its possession receipts for
any Taxes paid to foreign Tax authorities. Neither Company nor any Company
Subsidiary has ever been a "personal holding company" within the meaning of
Section 542 of the Code or a "United Sates real property holding corporation"
within the meaning of Section 897 of the Code.

    SECTION 4.16  Insurance

    Company and each Company Subsidiary is presently insured, and during each of
the past three calendar years has been insured, against such risks, as to the
Company's knowledge, that companies engaged in a similar business would, in
accordance with good business practice, customarily be insured. The policies of
fire, theft, liability and other insurance maintained with respect to the assets
or businesses of Company and Company Subsidiaries provide, to the Company's
knowledge, adequate coverage against loss. Company has heretofore made available
to Parent a complete and correct list as of the date hereof of all insurance
policies maintained by Company or the Company Subsidiaries, and has made
available to Parent complete and correct copies of all such policies, together
with all riders and amendments thereto. All such policies are in full force and
effect and all premiums due thereon have been paid to the date hereof. Company
and the Company Subsidiaries have complied in all material respects with the
terms of such policies.

    SECTION 4.17  Properties

    Company and the Company Subsidiaries have good title, free and clear of all
material mortgages, liens, pledges, charges or other encumbrances to all their
material tangible properties and assets, real, personal or mixed, reflected in
the Company's consolidated financial statements contained in the Company's
Annual Report on Form 10-K for the fiscal year ended December 31, 1998, as being
owned by Company and the Company Subsidiaries as of the date thereof, other than
(i) any properties or assets that have been sold or otherwise disposed of in the
ordinary course of business since the date of such financial statements,
(ii) liens disclosed in the notes to such financial statements and (iii) liens
arising in the ordinary course of business after the date of such financial
statements. All buildings, and all fixtures, equipment and other property and
assets that are material to its business on a consolidated basis, held under
leases or sub-leases by Company or any Company Subsidiary are held under valid
instruments enforceable in accordance with their respective terms, subject to
applicable laws of bankruptcy, insolvency or similar laws relating to creditors'
rights generally and to general principles of equity (whether applied in a
proceeding in law or equity). Substantially all of Company's and the Company
Subsidiaries' equipment in regular use has been reasonably maintained and is in
serviceable condition, reasonable wear and tear excepted.

    SECTION 4.18  Affiliates

    Section 4.18 of the Company Disclosure Schedule sets forth the name of each
person who is, in Company's reasonable judgment, an affiliate (as such term is
used in Rule 145 under the Securities Act or

                                      A-19
<PAGE>
under applicable SEC accounting releases with respect to pooling of interests
accounting treatment) of Company.

    SECTION 4.19  Opinion of Financial Advisor

    BancBoston Robertson Stephens Inc. ("Robertson Stephens") has delivered to
the board of directors of Company its written opinion to the effect that, as of
the date hereof, the Exchange Ratio is fair to the holders of shares of Company
Common Stock from a financial point of view (the "BRS Fairness Opinion").

    SECTION 4.20  Brokers

    No broker, finder or investment banker (other than Robertson Stephens) is
entitled to any brokerage, finder's or other fee or commission in connection
with the Merger based upon arrangements made by or on behalf of Company. Company
has heretofore made available to Parent true, complete and correct copies of all
agreements between Company and Robertson Stephens pursuant to which such firm
would be entitled to any payment relating to the Merger.

    SECTION 4.21  Certain Business Practices

    Neither Company nor any Company Subsidiary nor any directors, officers,
agents or employees of Company or any Company Subsidiary (in their capacities as
such) has (i) used any funds of the Company for unlawful contributions, gifts,
entertainment or other unlawful expenses relating to political activity or
(ii) made any unlawful payment by the Company to foreign or domestic government
officials or employees or to foreign or domestic political parties or campaigns
or violated any provision of the Foreign Corrupt Practices Act of 1977, as
amended.

    SECTION 4.22  Section 203 of the DGCL Not Applicable

    The Board of Directors of Company has approved the Merger, this Agreement,
the Option Agreement and the Stockholder Agreements, and such approval is
sufficient to render inapplicable to the Merger, this Agreement, the Option
Agreement and the Stockholder Agreements and the transactions contemplated by
this Agreement, the Option Agreement and the Stockholder Agreements the
provisions of Section 203 of the DGCL. To Company's knowledge, no other state
takeover statute or similar statute or regulation applies or purports to apply
to the Merger, this Agreement, the Option Agreement, the Stockholders Agreements
or the transactions contemplated by this Agreement, the Option Agreement and the
Stockholders Agreements.

    SECTION 4.23  Business Activity Restriction

    There is no non-competition or other similar agreement, commitment,
judgment, injunction, order or decree to which Company or any subsidiary of
Company is a party or subject to that has or could reasonably be expected to
have the effect of prohibiting or impairing the conduct of business by Company.
Company has not entered into any agreement under which Company is restricted in
any material respect from selling, licensing or otherwise distributing any of
its technology or products to, or providing services to, customers or potential
customers or any class of customers, in any geographic area, during any period
of time or in any segment of the market or line of business.

                                   ARTICLE V
                    REPRESENTATIONS AND WARRANTIES OF PARENT

    Parent hereby represents and warrants to Company, subject to the exceptions
specifically disclosed in the Parent Disclosure Schedule, all such exceptions to
be referenced to a specific representation set forth

                                      A-20
<PAGE>
in this Article V or to otherwise be clearly applicable to representations
hereof not specifically referenced, that:

    SECTION 5.01  Organization and Qualification; Subsidiaries

    (a) Parent and each directly and indirectly owned subsidiary of Parent (the
"Parent Subsidiaries") has been duly organized and is validly existing and in
good standing (to the extent applicable) under the laws of the jurisdiction of
its incorporation or organization, as the case may be, and has the requisite
corporate power and authority and all necessary governmental approvals to own,
lease and operate its properties and to carry on its business as it is now being
conducted. Parent, and each Parent Subsidiary is duly qualified or licensed to
do business, and is in good standing (to the extent applicable), in each
jurisdiction where the character of the properties owned, leased or operated by
it or the nature of its business makes such qualification or licensing
necessary.

    (b) Section 5.01 of the Parent Disclosure Schedule sets forth, as of the
date of this Agreement, a true and complete list of each Parent Subsidiary,
together with (i) the jurisdiction of incorporation or organization of each
Parent Subsidiary and the percentage of each Parent Subsidiary's outstanding
capital stock or other equity interests owned by Parent or another Parent
Subsidiary and (ii) an indication of whether each Parent Subsidiary is a
"Significant Subsidiary" as defined in Regulation S-X under the Exchange Act.
Neither Parent nor any Parent Subsidiary owns an equity interest in any
partnership or joint venture arrangement or other business entity that is
material to the business, assets, liabilities, financial condition or results of
operations of Parent and the Parent Subsidiaries, taken as a whole.

    SECTION 5.02  Certificate of Incorporation and Bylaws

    The copies of each of Parent's and Merger Subs' certificate of incorporation
and bylaws previously provided to Company by Parent are true, complete and
correct copies thereof. Such certificates of incorporation and bylaws are in
full force and effect.

    SECTION 5.03  Capitalization

    The authorized capital stock of Parent consists of 400,000,000 shares of
Parent Common Stock and 5,000,000 shares of preferred stock. As of June 4, 1999
(which numbers are not materially different on the date hereof) (i) 39,703,267
shares of Parent Common Stock are issued and outstanding, all of which are
validly issued, fully paid and nonassessable, (ii) no shares of Parent Common
Stock are held in the treasury of the Company, (iii) no shares of Parent Common
Stock are held by the Parent Subsidiaries, (iv) 5,455,188 shares of Parent
Common Stock are reserved for future issuance pursuant to outstanding options
and warrants to purchase Parent Common Stock ("Parent Stock Option"), and
(v) no shares of Parent preferred stock are issued and outstanding. Except for
the shares of Parent Common Stock issuable pursuant to the Parent Stock Plans,
there are no options, warrants or other rights, agreements, arrangements or
commitments of any character to which Parent is a party or by which Parent is
bound relating to the issued or unissued capital stock of Parent or any Parent
Subsidiary or obligating Parent or any Parent Subsidiary to issue or sell any
shares of capital stock of, or other equity interests in, Parent or any Parent
Subsidiary. All shares of Parent Common Stock subject to issuance as aforesaid,
upon issuance prior to the Effective Time on the terms and conditions specified
in the instruments pursuant to which they are issuable, will be duly authorized,
validly issued, fully paid and nonassessable. There are no outstanding
contractual obligations of Parent or any Parent Subsidiary to repurchase, redeem
or otherwise acquire any shares of Parent Common Stock or any capital stock of
any Parent Subsidiary. Each outstanding share of capital stock of each Parent
Subsidiary is duly authorized, validly issued, fully paid and nonassessable and
each such share owned by Parent or another Parent Subsidiary is free and clear
of all security interests, liens, claims, pledges, options, rights of first
refusal, agreements, limitations on Parent's or such other Parent Subsidiary's
voting rights, charges and other encumbrances of any nature whatsoever. There
are no material outstanding contractual obligations of Parent or any Parent
Subsidiary to provide funds to, or

                                      A-21
<PAGE>
make any material investment (in the form of a loan, capital contribution or
otherwise) in, any Parent Subsidiary or any other person.

    SECTION 5.04  Authority Relative to this Agreement

    Each of Parent and Merger Sub has all necessary corporate power and
authority to execute and deliver this Agreement, to perform its obligations
hereunder and to consummate the transactions contemplated hereby. The execution
and delivery of this Agreement by each of Parent and Merger Sub and the
consummation by Parent and Merger Sub of the transactions contemplated hereby
have been duly and validly authorized by all necessary corporate action, and no
other corporate proceedings on the part of Parent or Merger Sub are necessary to
authorize this Agreement or to consummate such transactions (other than the
approval of this Agreement and the Merger by the holders of a majority of the
outstanding shares of Parent Common Stock present at the Parent Shareholders'
Meeting and the consent of Parent as sole stockholder of Merger Sub). This
Agreement has been duly executed and delivered by each of Parent and Merger Sub
and, assuming the due authorization, execution and delivery by Company,
constitutes a legal, valid and binding obligation of each of Parent and Merger
Sub enforceable against Parent and Merger Sub in accordance with its terms.

    SECTION 5.05  No Conflict; Required Filings and Consents

    (a) The execution and delivery of this Agreement by Parent and Merger Sub
does not, and the performance by Parent and Merger Sub of their obligations
hereunder and the consummation of the Merger will not, (i) conflict with or
violate any provision of the articles of incorporation or bylaws of Parent or
any equivalent organizational documents of any Parent Subsidiary, (ii) assuming
that all consents, approvals, authorizations and permits described in Section
5.05(b) have been obtained and all filings and notifications described in
Section 5.05(b) have been made, conflict with or violate any Law applicable to
Parent or any other Parent Subsidiary or by which any property or asset of
Parent or any Parent Subsidiary is bound or affected or (iii) result in any
material breach of or constitute a material default (or an event which with the
giving of notice or lapse of time or both could reasonably be expected to become
a default) under, or give to others any right of termination, amendment,
acceleration or cancellation of, or result in the creation of a lien or other
encumbrance on any material property or asset of Parent or any Parent Subsidiary
pursuant to, any material note, bond, mortgage, indenture, contract, agreement,
lease, license, permit, franchise or other instrument or obligation.

    (b) Except as may arise solely from the nature of Company's business, the
execution and delivery of this Agreement by Parent and Merger Sub does not, and
the performance by Parent and Merger Sub of their obligations hereunder and the
consummation of the Merger will not, require any consent, approval,
authorization or permit of, or filing by Parent with or notification by Parent
to, any Governmental Entity, except pursuant to applicable requirements of the
Exchange Act, the Securities Act, Blue Sky Laws, the rules and regulations of
the NNM, state takeover laws, the premerger notification requirements of the HSR
Act, if any, and the filing and recordation of the Certificate of Merger as
required by the DGCL.

    SECTION 5.06  SEC Filings; Financial Statements

    (a) Parent has timely filed all forms, reports, statements and documents
required to be filed by it (A) with the SEC and the NNM since March 1, 1998
(collectively, together with any such forms, reports, statements and documents
Parent may file subsequent to the date hereof until the Closing, the "Parent
Reports") and (B) with any other Governmental Entities. Each Parent Report
(i) was prepared in accordance with the requirements of the Securities Act, the
Exchange Act or the NNM, as the case may be, substantially in all respects and
(ii) did not at the time it was filed contain any untrue statement of a material
fact or omit to state a material fact required to be stated therein or necessary
in order to make the statements made therein, in the light of the circumstances
under which they were made, not misleading. Each form, report, statement and
document referred to in clause (B) of this paragraph was prepared in all
material respects in accordance with the requirements of applicable Law. No
Parent Subsidiary is subject

                                      A-22
<PAGE>
to the periodic reporting requirements of the Exchange Act or required to file
any form, report or other document with the SEC, the NNM, any other stock
exchange or any other comparable Governmental Entity.

    (b) Except as is provided in the Parent Reports, each of the consolidated
financial statements (including, in each case, any notes thereto) contained in
the Parent Reports was prepared in accordance with U.S. GAAP applied on a
consistent basis throughout the periods indicated (except as may be indicated in
the notes thereto) and each presented fairly, in all material respects, the
consolidated financial position of Parent and the consolidated Parent
Subsidiaries as at the respective dates thereof and for the respective periods
indicated therein, except as otherwise noted therein (subject, in the case of
unaudited statements, to normal and recurring immaterial year-end adjustments).

    (c) Except as and to the extent set forth or reserved against on the
consolidated balance sheet of Parent and the Parent Subsidiaries as reported in
the Parent Reports, including the notes thereto, none of Parent or any Parent
Subsidiary has any liabilities or obligations of any nature (whether accrued,
absolute, contingent or otherwise) that would be required to be reflected on a
balance sheet or in notes thereto prepared in accordance with U.S. GAAP, except
for liabilities or obligations incurred in the ordinary course of business
consistent with past practice since December 31, 1998 that have not had and
could not reasonably be expected to have, individually or in the aggregate, a
Parent Material Adverse Effect.

    SECTION 5.07  Pooling; Certain Tax Matters

    To Parent's knowledge, neither Parent nor any of its affiliates has taken or
agreed to take any action (other than actions contemplated by this Agreement)
that could reasonably be expected (based on the advice of
PricewaterhouseCoopers) to prevent the Merger from being treated for accounting
purposes as a "pooling of interests" in accordance with U.S. GAAP and the
accounting standards of the SEC. Neither Parent, nor to Parent's knowledge, any
of its affiliates, has taken or agreed to take any action (other than actions
contemplated by this Agreement) that could be expected to prevent the Merger
from constituting a "reorganization" under Section 368 of the Code. Parent is
not aware of any agreement, plan or other circumstance that could reasonably be
expected to prevent the Merger from being so treated as a "pooling of interests"
or from so qualifying as a reorganization under Section 368 of the Code.

    SECTION 5.08  Opinion of Financial Advisor

    Goldman, Sachs & Co. ("Goldman Sachs") has delivered to the board of
directors of Parent its written opinion to the effect that, as of the date
hereof, the Exchange Ratio is fair, from a financial point of view, to Parent.

    SECTION 5.09  Brokers

    No broker, finder or investment banker (other than Goldman Sachs) is
entitled to any brokerage, finder's or other fee or commission in connection
with the Merger based upon arrangements made by or on behalf of Parent. Parent
has heretofore made available to Company true, complete and correct copies of
all agreements between Parent and Goldman Sachs pursuant to which such firm
would be entitled to any payment relating to the Merger.

    SECTION 5.10  Affiliates

    Section 5.10 of the Parent Disclosure Schedule sets forth the name of each
person who is, in Parent's reasonable judgment, an affiliate (under applicable
SEC accounting releases with respect to pooling of interests accounting
treatment) of Parent.

    SECTION 5.11  No Parent Material Adverse Effect

    Since December 31, 1998, there has been no Parent Material Adverse Effect.

                                      A-23
<PAGE>
                                   ARTICLE VI
                                   COVENANTS

    SECTION 6.01  Conduct of Business by Company Pending the Closing

    Company agrees that, between the date of this Agreement and the Effective
Time, unless Parent shall otherwise agree in writing, and except as a result of
entering into this Agreement (x) the respective businesses of Company and the
Company Subsidiaries shall be conducted only in, and Company and the Company
Subsidiaries shall not take any action except in, the ordinary course of
business consistent with past practice and (y) Company shall use all reasonable
efforts to keep available the services of such of the current officers,
significant employees and consultants of Company and the Company Subsidiaries
and to preserve the current relationships of Company and the Company
Subsidiaries with such of the corporate partners, customers, suppliers and other
persons with which Company or any Company Subsidiary has significant business
relations in order to preserve substantially intact its business organization.
By way of amplification and not limitation, neither Company nor any Company
Subsidiary shall, between the date of this Agreement and the Effective Time,
directly or indirectly, do, or agree to do, any of the following without the
prior written consent of Parent and except as a result of entering into this
Agreement:

        (a) amend or otherwise change its certificate of incorporation or bylaws
    or equivalent organizational documents;

        (b) issue, sell, pledge, dispose of, grant, transfer, lease, license,
    guarantee or encumber, or authorize the issuance, sale, pledge, disposition,
    grant, transfer, lease, license or encumbrance of, (i) any shares of capital
    stock of Company or any Company Subsidiary of any class, or securities
    convertible into or exchangeable or exercisable for any shares of such
    capital stock, or any options, warrants or other rights of any kind to
    acquire any shares of such capital stock, or any other ownership interest
    (including, without limitation, any phantom interest), of Company or any
    Company Subsidiary, other than (A) the issuance of shares of Company Common
    Stock pursuant to the exercise of stock options theretofore outstanding as
    of the date of this Agreement or (B) the issuance of options to purchase up
    to 250,000 shares of Company Common Stock under the Company's 1999 Stock
    Incentive Plan, 200,000 shares of which may be issued to newly hired
    management employees and 50,000 shares of which may be issued to existing
    non-executive employees, or (ii) any property or assets of Company or any
    Company Subsidiary except entering into alliance agreements or providing
    products and services in the ordinary course of business consistent with
    past practice;

        (c) (i) acquire (including, without limitation, by merger,
    consolidation, or acquisition of stock or assets) any interest in any
    corporation, partnership, other business organization or person or any
    division thereof; (ii) incur any indebtedness for borrowed money or issue
    any debt securities or assume, guarantee or endorse, or otherwise as an
    accommodation become responsible for, the obligations of any person (other
    than Company and Company Subsidiaries) for borrowed money or make any loans
    or advances, other than routine employee loans to employees other than
    Company officers (not to exceed $1,000 to any individual), material to the
    business, assets, liabilities, financial condition or results of operations
    of Company and the Company Subsidiaries, taken as a whole, other than in the
    ordinary course of business consistent with past practice; (iii) terminate,
    cancel or request any material change in, or agree to any material change
    in, any Company Material Contract or other License Agreement; (iv) make or
    authorize any capital expenditure, other than capital expenditures in the
    ordinary course of business consistent with past practice that have been
    budgeted for fiscal year 1999 and disclosed in writing to Parent and that
    are not, in the aggregate, in excess of $3,000,000 for Company and the
    Company Subsidiaries taken as a whole; or (v) enter into or amend any
    contract, agreement, commitment or arrangement that, if fully performed,
    would not be permitted under this Section 6.01(c);

                                      A-24
<PAGE>
        (d) declare, set aside, make or pay any dividend or other distribution,
    payable in cash, stock, property or otherwise, with respect to any of its
    capital stock, except that any Company Subsidiary may pay dividends or make
    other distributions to Company or any other Company Subsidiary;

        (e) reclassify, combine, split, subdivide or redeem, purchase or
    otherwise acquire, directly or indirectly, any of its capital stock;

        (f) amend or change the period (or permit any acceleration, amendment or
    change unless required pursuant to the terms of existing agreements of
    Company previously provided to Parent) of exercisability of options granted
    under the Company Stock Plans or authorize cash payments in exchange for any
    Company Stock Options granted under any of such plans;

        (g) amend the terms of, repurchase, redeem or otherwise acquire, or
    permit any Company Subsidiary to repurchase, redeem or otherwise acquire,
    any of its securities or any securities of any Company Subsidiary or propose
    to do any of the foregoing;

        (h) other than in the ordinary course of business consistent with past
    practices or pursuant to existing agreements of Company previously provided
    to Parent increase the compensation payable or to become payable to its
    directors, officers, consultants or employees, grant any rights to severance
    or termination pay to, or enter into any employment or severance agreement
    which provides benefits upon a change in control of Company that would be
    triggered by the Merger with, any director, officer, consultant or other
    employee of Company or any Company Subsidiary who is not currently entitled
    to such benefits from the Merger, establish, adopt, enter into or amend any
    collective bargaining, bonus, profit sharing, thrift, compensation, stock
    option, restricted stock, pension, retirement, deferred compensation,
    employment, termination, severance or other plan, agreement, trust, fund,
    policy or arrangement for the benefit of any director, officer, consultant
    or employee of Company or any Company Subsidiary, except to the extent
    required by applicable Law or the terms of a collective bargaining
    agreement, or enter into or amend any contract, agreement, commitment or
    arrangement between Company or any Company Subsidiary and any of Company's
    directors, officers, consultants or employees;

        (i) pay, discharge or satisfy any claims, liabilities or obligations
    (absolute, accrued, asserted or unasserted, contingent or otherwise), other
    than the payment, discharge or satisfaction in the ordinary course of
    business and consistent with past practice of liabilities reflected or
    reserved against on the consolidated balance sheet of Company and the
    consolidated the Company Subsidiaries dated as of March 31, 1999 included in
    Company's quarterly report on Form 10-Q for the period then ended (the
    "Company Balance Sheet") and only to the extent reflected or to the extent
    of such reserves or incurred in the ordinary course of business since
    March 31, 1999;

        (j) make any change with respect to Company's accounting policies,
    principles, methods or procedures, including, without limitation, revenue
    recognition policies, other than as required by U.S. GAAP;

        (k) make any material Tax election or settle or compromise any material
    Tax liability; or

        (l) authorize or enter into any formal or informal agreement or
    otherwise make any commitment to do any of the foregoing or to take any
    action which would make any of the representations or warranties of Company
    contained in this Agreement untrue or incorrect in any material respect or
    result in any of the conditions to the Merger set forth herein not being
    satisfied.

    SECTION 6.02  Notices of Certain Events

    Each of Parent and Company shall give prompt notice to the other of (i) any
notice or other communication from any person alleging that the consent of such
person is or may be required in connection with the Merger; (ii) any notice or
other communication from any Governmental Entity in connection with the Merger;
(iii) any actions, suits, claims, investigations or proceedings commenced or, to

                                      A-25
<PAGE>
its knowledge, threatened against, relating to or involving or otherwise
affecting Parent or the Parent Subsidiaries or Company or the Company
Subsidiaries, respectively, or that relate to the consummation of the Merger;
(iv) the occurrence of a default or event that, with the giving of notice or
lapse of time or both, will become a default under any Parent Material Contract
or Company Material Contract, respectively; and (v) any change that could
reasonably be expected to have a Parent Material Adverse Effect or a Company
Material Adverse Effect, respectively, or to delay or impede the ability of
either Parent or Company, respectively, to perform their respective obligations
pursuant to this Agreement and to effect the consummation of the Merger.

    SECTION 6.03  Access to Information; Confidentiality

    (a) Except as required pursuant to any confidentiality agreement or similar
agreement or arrangement to which Parent or Company or any of the Parent
Subsidiaries or the Company Subsidiaries is a party or pursuant to applicable
Law or the regulations or requirements of any stock exchange or other regulatory
organization with whose rules a party hereto is required to comply, from the
date of this Agreement to the Effective Time, Parent and Company shall (and
shall cause the Parent Subsidiaries and Company Subsidiaries, respectively, to)
(i) provide to the other (and its officers, directors, employees, accountants,
consultants, legal counsel, agents and other representatives (collectively,
"Representatives")) access at reasonable times upon prior notice to its and its
subsidiaries' officers, employees, agents, properties, offices and other
facilities and to the books and records thereof, and (ii) furnish promptly such
information concerning its and its subsidiaries' business, properties,
contracts, assets, liabilities and personnel as the other party or its
Representatives may reasonably request. All such investigations and access shall
be conducted in a manner as not to interfere unreasonably with the business
operations of the Company. No investigation conducted pursuant to this Section
6.03 shall affect or be deemed to modify any representation or warranty made in
this Agreement.

    (b) The parties hereto shall comply with, and shall cause their respective
Representatives to comply with, all of their respective obligations under the
Confidentiality Agreements with respect to the information disclosed pursuant to
this Section 6.03 or pursuant to the Confidentiality Agreements.

    SECTION 6.04  No Solicitation of Transactions

    Until this Agreement has been terminated as provided herein, Company shall
not, directly or indirectly, and shall cause its Representatives not to,
directly or indirectly, solicit, initiate or encourage (including by way of
furnishing nonpublic information), any inquiries or the making of any proposal
or offer (including, without limitation, any proposal or offer to its
stockholders) that constitutes, or may reasonably be expected to lead to, any
Competing Transaction, or enter into or maintain or continue discussions or
negotiate with any person in furtherance of such inquiries or to obtain a
Competing Transaction, or agree to or endorse any Competing Transaction, or
authorize or permit any of Company's Representatives or subsidiaries, or any
Representative retained by Company's subsidiaries, to take any such action;
provided, however, that nothing contained in this Section 6.04 shall prohibit
the board of directors of Company (i) from complying with Rule 14d-9 or 14e-2(a)
promulgated under the Exchange Act with regard to a tender or exchange offer not
made in violation of this Section 6.04 or (ii) prior to receipt of the approval
by the stockholders of Company of this Agreement and the Merger from providing
information (subject to a confidentiality agreement at least as restrictive as
the Confidentiality Agreements) in connection with, and negotiating, another
unsolicited, bona fide written proposal regarding a Competing Transaction that
(x) Company's board of directors shall have concluded in good faith, after
considering applicable state law, on the basis of advice of independent outside
counsel that such action is necessary to prevent Company's board of directors
from violating its fiduciary duties to Company's stockholders under applicable
law, (y) if any cash consideration is involved, shall not be subject to any
financing contingency, and with respect to which Company's board of directors
shall have determined (based upon the advice of Company's independent financial
advisors) in the exercise of its fiduciary duties

                                      A-26
<PAGE>
to Company's stockholders that the acquiring party is capable of consummating
such Competing Transaction on the terms proposed, and (z) Company's board of
directors shall have determined in the exercise of its fiduciary duties to
Company's stockholders that such Competing Transaction provides greater value to
the stockholders of Company than the Merger (based upon the written opinion of
Company's independent financial advisors that such Competing Transaction is
superior from a financial point of view) (any such Competing Transaction being
referred to herein as a "Superior Proposal"). Any violation of the restrictions
set forth in this Section 6.04 by any Representative of Company or any of its
Subsidiaries, whether or not such Person is purporting to act on behalf of
Company or otherwise, shall be deemed to be a breach of this Section 6.04 by
Company. Company shall notify Parent promptly if any proposal or offer, or any
inquiry or contact with any person with respect thereto, regarding a Competing
Transaction is made, such notice to include the identity of the person making
such proposal, offer, inquiry or contact, and the terms of such Competing
Transaction, and shall keep Parent apprised, on a current basis, of the status
of such Competing Transaction and of any modifications to the terms thereof.
Company immediately shall cease and cause to be terminated all existing
discussions or negotiations with any parties conducted heretofore with respect
to a Competing Transaction. Company shall not release any third party from, or
waive any provision of, any confidentiality or standstill agreement to which it
is a party.

    SECTION 6.05  Tax-Free Transaction; Pooling

    From and after the date of this Agreement, each party hereto shall use all
reasonable efforts to cause the Merger to qualify, and shall not knowingly take
any actions or cause any actions to be taken which could reasonably be expected
to prevent the Merger from (a) qualifying as a "reorganization" under Section
368(a) of the Code or (b) being treated for financial accounting purposes as a
"pooling of interests" in accordance with U.S. GAAP and the accounting standards
of the SEC.

    SECTION 6.06  Control of Operations

    Nothing contained in this Agreement shall give Parent, directly or
indirectly, the right to control or direct the operations of Company and the
Company Subsidiaries prior to the Effective Time. Prior to the Effective Time,
Company shall exercise, consistent with the terms and conditions of this
Agreement, complete control and supervision over its operations.

    SECTION 6.07  Further Action; Consents; Filings

    (a) Upon the terms and subject to the conditions hereof, each of the parties
hereto shall use all reasonable efforts to (i) take, or cause to be taken, all
appropriate action, and do, or cause to be done, all things necessary, proper or
advisable under applicable Law or otherwise to consummate and make effective the
Merger, (ii) obtain from Governmental Entities any consents, licenses, permits,
waivers, approvals, authorizations or orders required to be obtained or made by
Parent or Company or any of their respective subsidiaries in connection with the
authorization, execution and delivery of this Agreement and the consummation of
the Merger and (iii) make all necessary filings, and thereafter make any other
required or appropriate submissions, with respect to this Agreement and the
Merger required under (A) the rules and regulations of the NNM, (B) the
Securities Act, the Exchange Act and any other applicable Federal or state
securities Laws, (C) the HSR Act, if any, and (D) any other applicable Law. The
parties hereto shall cooperate and consult with each other in connection with
the making of all such filings, including by providing copies of all such
documents to the nonfiling parties and their advisors prior to filing, and none
of the parties shall file any such document if any of the other parties shall
have reasonably objected to the filing of such document. No party shall consent
to any voluntary extension of any statutory deadline or waiting period or to any
voluntary delay of the consummation of the Merger at the behest of any
Governmental Entity without the consent and agreement of the other parties
hereto, which consent shall not be unreasonably withheld or delayed.

    (b) Each of company and Parent will give (or will cause their respective
subsidiaries to give) any notices to third persons, and use, and cause their
respective subsidiaries to use, reasonable efforts to obtain

                                      A-27
<PAGE>
any consents from third persons necessary, proper or advisable (as determined in
good faith by Parent with respect to such notices or consents to be delivered or
obtained by Company) to consummate the transactions contemplated by this
Agreement.

    SECTION 6.08  Additional Reports

    Company and Parent shall each furnish to the other copies of any reports of
the type referred to in Sections 4.07 and 5.06, which it files with the SEC on
or after the date hereof, and Company and Parent, as the case may be, covenant
and warrant that as of the respective dates thereof, such reports will not
contain any untrue statement of a material fact or omit to state a material fact
required to be stated therein or necessary to make the statements therein, in
light of the circumstances under which they were made, not misleading. Any
unaudited consolidated interim financial statements included in such reports
(including any related notes and schedules) will fairly present in all material
respects the financial position of Company and its consolidated subsidiaries or
Parent and its consolidated subsidiaries, as the case may be, as of the dates
thereof and the results of operations and changes in financial position or other
information including therein for the periods or as of the date then ended
(subject, where appropriate, to normal year-end adjustments), in each case in
accordance with past practice and U.S. GAAP consistently applied during the
periods involved (except as otherwise disclosed in the notes thereto).

    SECTION 6.09  Tax Information

    Company shall provide the following information to Parent not later than
four weeks after the date of this Agreement: (i) a complete list of the types of
Tax Returns being filed by Company and each Company Subsidiary in each taxing
jurisdiction, (ii) a list of all closed years with respect to each such type of
Tax Return filed in each jurisdiction, and (iii) a list of any deferred
intercompany gain with respect to transactions to which Company or any Company
Subsidiary has been a party. Company shall provide Parent and its accountants,
counsel and other representatives reasonable access, during normal business
hours during the period prior to the Effective Time, to all of Company's and
Company Subsidiaries' Tax Returns and other records and workpapers relating to
Taxes.

    SECTION 6.10  Conduct of Business by Parent

    During the period from the date of this Agreement and continuing until the
earlier of the termination of this Agreement pursuant to its terms or the
Effective Time, Parent shall not knowingly take any action a principal purpose
of which is, and the reasonably likely result of which would be, a material
delay in or interference with the consummation of the Merger.

                                  ARTICLE VII
                             ADDITIONAL AGREEMENTS

    SECTION 7.01  Registration Statement; Joint Proxy Statement

    (a) As promptly as practicable after the execution of this Agreement, Parent
and Company shall jointly prepare and shall file with the SEC a document or
documents that will constitute (i) the prospectus forming part of the
registration statement on Form S-4 of Parent (together with all amendments
thereto, the "Registration Statement"), in connection with the registration
under the Securities Act of Parent Common Stock to be issued to Company's
stockholders pursuant to the Merger and (ii) the joint proxy statement with
respect to the Merger relating to the special meetings of Company's stockholders
to be held to consider approval of this Agreement and the Merger (the "Company
Stockholders' Meeting") and of Parent's stockholders to be held to consider
approval of the issuance of Parent Common Stock (the "Share Issuance") to
Company's stockholders pursuant to the Merger (the "Parent Stockholders'
Meeting") (together with any amendments thereto, the "Joint Proxy Statement").
Copies of the Joint Proxy Statement shall be provided to the NNM in accordance
with its rules. Each of the parties hereto shall use all reasonable efforts to
cause the Registration Statement to become effective as promptly as practicable
after

                                      A-28
<PAGE>
the date hereof, and, prior to the effective date of the Registration Statement,
the parties hereto shall take all action required under any applicable Laws in
connection with the issuance of shares of Parent Common Stock pursuant to the
Merger. Parent or Company, as the case may be, shall furnish all information
concerning Parent or Company as the other party may reasonably request in
connection with such actions and the preparation of the Registration Statement
and the Joint Proxy Statement. As promptly as practicable after the effective
date of the Registration Statement, the Joint Proxy Statement shall be mailed to
the stockholders of Company and of Parent. Each of the parties hereto shall
cause the Joint Proxy Statement to comply as to form and substance as to such
party in all material respects with the applicable requirements of (i) the
Exchange Act, (ii) the Securities Act, (iii) the rules and regulations of the
NNM.

    (b) The Joint Proxy Statement shall include (i) the approval of the Merger
and the recommendation of the board of directors of Company to Company's
stockholders that they vote in favor of approval of this Agreement and the
Merger, subject to the right of the board of directors of the Company to
withdraw its recommendation and recommend a Superior Proposal in compliance with
Section 6.04 of this Agreement, and (ii) the opinion of Robertson Stephens
referred to in Section 4.19; provided, however, that the board of directors of
Company shall submit this Agreement to Company's stockholders whether or not at
any time subsequent to the date hereof such board determines that it can no
longer make such recommendation. The Joint Proxy Statement shall include
(A) the approval of the Share Issuance and the recommendation of the board of
directors of Parent to Parent's stockholders that they vote in favor of approval
of the Share Issuance, and (B) the opinion of Goldman Sachs referred to in
Section 5.08.

    (c) No amendment or supplement to the Joint Proxy Statement or the
Registration Statement shall be made without the approval of Parent and Company,
which approval shall not be unreasonably withheld or delayed. Each of the
parties hereto shall advise the other parties hereto, promptly after it receives
notice thereof, of the time when the Registration Statement has become effective
or any supplement or amendment has been filed, of the issuance of any stop
order, of the suspension of the qualification of the Parent Common Stock
issuable in connection with the Merger for offering or sale in any jurisdiction,
or of any request by the SEC for amendment of the Joint Proxy Statement or the
Registration Statement or comments thereon and responses thereto or requests by
the SEC for additional information.

    (d) None of the information supplied by Company for inclusion or
incorporation by reference in the Registration Statement or the Joint Proxy
Statement shall, at the respective times filed with the SEC or other regulatory
agency and, in addition, (A) in the case of the Joint Proxy Statement, at the
date it or any amendments or supplements thereto are mailed to stockholders of
Parent and Company, at the time of the Company Stockholders' Meeting, at the
time of the Parent Shareholders' Meeting and at the Effective Time and (B) in
the case of the Registration Statement, when it becomes effective under the
Securities Act and at the Effective Time, contain any untrue statement of a
material fact or omit to state any material fact required to be stated therein
or necessary in order to make the statements therein, in light of the
circumstances under which they are made, not misleading. If at any time prior to
the Effective Time any event or circumstance relating to Company or any Company
Subsidiary, or their respective officers or directors, should be discovered by
Company that should be set forth in an amendment or a supplement to the
Registration Statement or the Joint Proxy Statement, Company shall promptly
inform Parent. All documents that Company is responsible for filing with the SEC
in connection with the Merger will comply as to form in all material respects
with the applicable requirements of the rules and regulations of the Securities
Act and the Exchange Act.

    (e) None of the information supplied by Parent for inclusion or
incorporation by reference in the Registration Statement or the Joint Proxy
Statement shall, at the respective times filed with the SEC or other regulatory
agency and, in addition, (A) in the case of the Joint Proxy Statement, at the
date it or any amendments or supplements thereto are mailed to stockholders of
Parent and Company, at the time of Company Stockholders' meeting, at the time of
the Parent Shareholders' Meeting and at the Effective Time and (B) in the case
of the Registration Statement, when it becomes effective under the Securities
Act

                                      A-29
<PAGE>
and at the Effective Time, contain any untrue statement of a material fact or
omit to state any material fact required to be stated therein or necessary in
order to make the statements therein, in light of the circumstances under which
they are made, not misleading. If, at any time prior to the Effective Time, any
event or circumstance relating to Parent or any Parent Subsidiary, or their
respective officers or directors, should be discovered by Parent that should be
set forth in an amendment or a supplement to the Registration Statement or the
Joint Proxy Statement, Parent shall promptly inform Company. All documents that
Parent is responsible for filing with the SEC in connection with the Merger will
comply as to form in all material respects with the applicable requirements of
the rules and regulations of the Securities Act and the Exchange Act.

    SECTION 7.02  Stockholders' Meetings

    Company shall call and hold the Company Stockholders' Meeting and Parent
shall call and hold the Parent Stockholders' Meeting as promptly as practicable
after the date hereof for the purpose of voting upon the approval of this
Agreement and the Merger or the Share Issuance, as the case may be, pursuant to
the Joint Proxy Statement, and Company and Parent shall use all reasonable
efforts to hold the Parent Stockholders' Meeting and the Company Stockholders'
Meeting on the same day and as soon as practicable after the date on which the
Registration Statement becomes effective. Nothing herein shall prevent the
Company or the Parent from adjourning or postponing the Company Stockholders'
Meeting or the Parent Stockholders' Meeting, as the case may be, if there are
insufficient shares of Company Common Stock or Parent Common Stock, as the case
may be, necessary to conduct business at their respective meetings of the
stockholders. Unless Company's board of directors has withdrawn its
recommendation of this Agreement and the Merger in compliance with Section 6.04,
Company shall use all reasonable efforts to solicit from its stockholders
proxies in favor of the approval of this Agreement and the Merger pursuant to
the Joint Proxy Statement and shall take all other action necessary or advisable
to secure the vote or consent of stockholders required by the DGCL or applicable
other stock exchange requirements to obtain such approval. Parent shall use all
reasonable efforts to solicit from its stockholders proxies in favor of the
Share Issuance pursuant to the Joint Proxy Statement and shall take all other
action necessary or advisable to secure the vote or consent of stockholders
required by the DGCL or applicable stock exchange requirements to obtain such
approval. Each of the parties hereto shall take all other action necessary or,
in the opinion of the other parties hereto, advisable to promptly and
expeditiously secure any vote or consent of stockholders required by applicable
Law and such party's certificate of incorporation and bylaws to effect the
Merger. Company shall call and hold the Company Stockholders' Meeting for the
purpose of voting upon the approval of this Agreement and the Merger whether or
not Company's board of directors at any time subsequent to the date hereof
determines that this Agreement is no longer advisable or recommends that
Company's stockholders reject it.

    SECTION 7.03  Affiliates

    (a) Company will use reasonable efforts to obtain an executed letter
agreement substantially in the form of Annex C hereto from (i) each person
identified in Section 4.18 of the Company Disclosure Schedule within 15 days
following the execution and delivery of this Agreement and (ii) from any person
who, to the knowledge of Company, may be deemed to have become an affiliate of
Company after the date of this Agreement and prior to the Effective Time as soon
as practicable after attaining such status. The foregoing notwithstanding,
Parent shall be entitled to place legends as specified in the Affiliate
Agreement on the certificates evidencing any of the Parent Common Stock to be
received by (i) any affiliate of Company or (ii) any person Parent reasonably
identifies (by written notice to Company) as being a person who is an
"affiliate" within the meaning of Rule 145 promulgated under the Securities Act,
and to issue appropriate stop transfer instructions to the transfer agent for
such Parent Common Stock, consistent with the terms of the Affiliate Agreement,
regardless of whether such person has executed Affiliate Agreement and
regardless of whether such person's name and address appear on Section 4.18 of
the Company Disclosure Schedule.

                                      A-30
<PAGE>
    (b) Parent will use reasonable efforts to obtain an executed letter
agreement substantially in the form of Annex D hereto from (i) each person
identified in Section 5.10 of the Parent Disclosure Schedule within 15 days
following the execution and delivery of this Agreement and (ii) from any person
who, to the knowledge of Parent, is an affiliate of Parent after the date of
this Agreement and prior to the Effective Time as soon as practicable after
attaining such status.

    SECTION 7.04  Directors' and Officers' Indemnification and Insurance

    (a) Parent and the Merger Sub agree that all rights to indemnification,
advancement of expenses, exculpation, limitation of liability and any and all
similar rights now existing in favor of each present and former director,
officer, employee and agent of Company and each Company Subsidiary
(collectively, the "Indemnified Parties") as provided in the Company's present
charter or by-laws in effect on the date hereof, shall survive the Merger and
shall continue in full force and effect for a period of six years from the
Effective Time, which provisions shall not be amended, repealed or otherwise
modified for a period of six years from the Effective Time in any manner that
would affect adversely the rights thereunder of individuals who at any time
prior to the Effective Time were directors, officers, employees or agents of the
Company, unless such modification shall be required by law, and Parent agrees to
cause the Surviving Corporation to comply with its obligations thereunder;
provided, however, that in the event any claim or claims are asserted or made
within such six-year period, all rights to indemnification in respect to any
such claim or claims shall continue until the disposition of any and all such
claims.

    (b) In the event the Company or the Surviving Corporation or any of their
respective successors or assigns (i) consolidates with or merges into any other
person and shall not be the continuing or Surviving Corporation or entity of
such consolidation or merger or (ii) transfers a material amount of its
properties and assets to any person in a single transaction or a series of
transactions, then, and in each such case, Parent will either guaranty the
indemnification obligations referred to in this Section 7.04 or will make or
cause to be made proper provision so that the successors and assigns of the
Company or the Surviving Corporation, as the case may be, assume the
indemnification obligations described herein for the benefit of the Indemnified
Parties and have substantially equal financial ability as the Company
(immediately prior to the Effective Time) to satisfy the obligations of the
parties pursuant to this Section 7.04 as a condition to such merger,
consolidation or transfer becoming effective.

    (c) The provisions of this Section 7.04 are (i) intended to be for the
benefit of, and will be enforceable by, each of the Indemnified Parties and
(ii) in addition to, and not in substitution for, any other rights to
indemnification or contribution that any such person may have by contract or
otherwise.

    (d) For a period of six years after the Effective Time, Parent shall
maintain in effect the directors' and officers' liability insurance policies
maintained by Company or, if not available, directors' and officers' liability
insurance policies covering the directors and officers of the Company (and their
respective heirs and executors, if such coverage may be obtained at no
additional cost) as of the date hereof, with coverages and other terms
substantially as favorable to such directors and officers as is currently in
effect; provided, however, that in no event shall Parent be required to expend
in any one year in excess of 150% of the annual premium currently paid by
Company for such coverage, which current premium amount is set forth in Section
7.04 of the Company Disclosure Schedule, and if the premium for such coverage
exceeds such amount, Parent shall purchase a policy with the greatest coverage
available for such 150% of the annual premium.

    SECTION 7.05  No Shelf Registration

    Parent shall not be required to amend or maintain the effectiveness of the
Registration Statement for the purpose of permitting resale of the shares of
Parent Common Stock received pursuant hereto by the persons who may be deemed to
be "affiliates" of Company within the meaning of Rule 145 promulgated under the
Securities Act.

                                      A-31
<PAGE>
    SECTION 7.06  Public Announcements

    The initial press release concerning the Merger shall be a joint press
release and, thereafter, Parent and Company shall consult with each other before
issuing any press release or otherwise making any public statements with respect
to this Agreement or the Merger and shall not issue any such press release or
make any such public statement without the prior written approval of the other,
except to the extent required by applicable Law or the requirements of the
rules and regulations of the NNM, in which case the issuing party shall use all
reasonable efforts to consult with the other party before issuing any such
release or making any such public statement.

    SECTION 7.07  NNM Listing

    Prior to the Effective Time, Parent shall file with the NNM a Notification
Form for Listing of Additional Shares with respect to the Parent Common Stock
issued or issuable in connection with the Merger.

    SECTION 7.08  Blue Sky

    Parent shall use all reasonable efforts to obtain prior to the Effective
Time all necessary permits and approvals required under Blue Sky Laws to permit
the distribution of the shares of Parent Common Stock to be issued in accordance
with the provisions of this Agreement.

    SECTION 7.09  Employee Benefit Matters

    At Parent's request, Company shall take all action necessary to terminate,
or cause to terminate, immediately before the Effective Time, any Company
Benefit Plan that is a 401(k) plan or other defined contribution retirement
plan.

                                  ARTICLE VIII
                            CONDITIONS TO THE MERGER

    SECTION 8.01  Conditions to the Obligations of Each Party to Consummate the
Merger

    The obligations of the parties hereto to consummate the Merger are subject
to the satisfaction or, if permitted by applicable Law, waiver of the following
conditions:

        (a) the Registration Statement shall have been declared effective by the
    SEC under the Securities Act and no stop order suspending the effectiveness
    of the Registration Statement shall have been issued by the SEC and no
    proceeding for that purpose shall have been initiated by the SEC and not
    concluded or withdrawn;

        (b) this Agreement and the Merger shall have been duly approved by the
    requisite vote of stockholders of Company in accordance with the DGCL and by
    the requisite vote of the stockholders of Parent in accordance with the
    rules of the NNM;

        (c) no court of competent jurisdiction shall have issued or entered any
    order, writ, injunction or decree, and no other Governmental Entity shall
    have issued any order, which is then in effect and has the effect of making
    the Merger illegal or otherwise prohibiting its consummation;

        (d) any waiting period (and any extension thereof) applicable to the
    consummation of the Merger under the HSR Act or any other applicable
    competition, merger control or similar Law shall have expired or been
    terminated;

        (e) all consents, approvals and authorizations legally required to be
    obtained to consummate the Merger shall have been obtained from all
    Governmental Entities, except where the failure to obtain any such consent,
    approval or authorization could not reasonably be expected to result in a
    Parent Material Adverse Effect or a Company Material Adverse Effect; and

                                      A-32
<PAGE>
        (f) The shares of Parent Common Stock to be issued in the Merger shall
    have been authorized for listing on the NNM, subject to notice of issuance.

    SECTION 8.02  Conditions to the Obligations of Company

    The obligations of Company to consummate the Merger, or to permit the
consummation of the Merger are subject to the satisfaction or, if permitted by
applicable Law, waiver of the following further conditions:

        (a) each of the representations and warranties of Parent contained in
    this Agreement shall be true, complete and correct in all respects both when
    made and on and as of the Effective Time as if made at and as of the
    Effective Time (other than representations and warranties which address
    matters only as of a certain date which shall be so true, complete and
    correct as of such certain date), except for any failures to be true,
    complete and correct which do not, in the aggregate, have a Parent Material
    Adverse Effect, and Company shall have received a certificate of the Chief
    Executive Officer and Chief Financial Officer of Parent to such effect;

        (b) Parent shall have performed or complied in all material respects
    with all covenants required by this Agreement to be performed or complied
    with by it on or prior to the Effective Time and Company shall have received
    a certificate of the Chief Executive Officer and Chief Financial Officer of
    Parent to that effect; and

        (c) Kane Kessler, P.C., special counsel to Company, or such other law
    firm or professional services firm reasonably acceptable to Parent
    (including any "Big 5" accounting firm) shall have issued its opinion, such
    opinion dated on the date of the Closing, addressed to Company, and
    reasonably satisfactory to it, based upon customary representations of
    Company and Parent and customary assumptions, to the effect that the Merger
    will constitute a "reorganization" within the meaning of Section 368(a) of
    the Code, which opinion shall not have been withdrawn or modified in any
    material respect; provided, however, that if such firm does not render such
    opinion, this condition shall nonetheless be deemed satisfied if such
    opinion, dated as of the date of the Closing, is rendered to Company by
    Brobeck, Phleger & Harrison LLP, counsel to Parent.

    SECTION 8.03  Conditions to the Obligations of Parent

    The obligations of Parent to consummate the Merger are subject to the
satisfaction or waiver of the following further conditions:

        (a) each of the representations and warranties of Company contained in
    this Agreement shall be true, complete and correct in all respects both when
    made and on and as of the Effective Time as if made at and as of the
    Effective Time (other than representations and warranties which address
    matters only as of a certain date which shall be so true, complete and
    correct as of such certain date), except for any failures to be true,
    complete and correct which do not, in the aggregate, have a Company Material
    Adverse Effect, and Parent shall have received a certificate of the Chief
    Executive Officer and Chief Financial Officer of Company to such effect;

        (b) Company shall have performed or complied in all material respects
    with all covenants required by this Agreement to be performed or complied
    with by it on or prior to the Effective Time and Parent shall have received
    a certificate of the Chief Executive Officer and Chief Financial Officer of
    Company to that effect;

        (c) Brobeck, Phleger & Harrison LLP, special counsel to Parent, shall
    have issued its opinion, such opinion dated on the date of the Closing,
    addressed to Parent, and reasonably satisfactory to it, based upon customary
    representations of Company and Parent and customary assumptions, to the
    effect that the Merger will constitute a "reorganization" within the meaning
    of Section 368(a) of the Code, which opinion shall not have been withdrawn
    or modified in any material respect;

                                      A-33
<PAGE>
        (d) Parent shall have been advised in writing by PricewaterhouseCoopers
    LLP--New York, NY as of the date upon which the Effective Time is to occur,
    in a form and in substance reasonably acceptable to Parent, that the Merger
    can properly be accounted for as a "pooling of interests" business
    combination in accordance with U.S. GAAP and the accounting standards of the
    SEC; Company shall have been advised in writing by PricewaterhouseCoopers
    LLP--Broomfield, CO as of the date upon which the Effective Time is to occur
    that such firm concurs with the management of the Company that no conditions
    exist that would preclude Company from being a party to a merger for which
    the pooling of interests method of accounting would be available;

        (e) There shall have been no Company Material Adverse Effect since the
    date of this Agreement;

        (f) All consents of third parties required pursuant to the terms of any
    Material Contract as a result of the Merger shall have been obtained; and

        (g) the employees of Company set forth on Schedule 8.03(g) shall have
    accepted employment with Parent and shall have entered into employment and
    non-competition agreements substantially in the form attached hereto as
    Annex E.

                                   ARTICLE IX
                       TERMINATION, AMENDMENT AND WAIVER

    SECTION 9.01  Termination

    This Agreement may be terminated and the Merger may be abandoned at any time
prior to the Effective Time, notwithstanding any requisite adoption and approval
of this Agreement, as follows:

        (a) by mutual written consent duly authorized by the boards of directors
    of each of Parent and Company;

        (b) by either Parent or Company, if the Effective Time shall not have
    occurred on or before December 31, 1999; provided, however, that the right
    to terminate this Agreement under this Section 9.01(b) shall not be
    available to any party whose failure to fulfill any obligation under this
    Agreement shall have principally caused, or resulted in, the failure of the
    Effective Time to occur on or before such date;

        (c) by either Parent or Company, if any Governmental Order, writ,
    injunction or decree preventing the consummation of the Merger shall have
    been entered by any court of competent jurisdiction and shall have become
    final and nonappealable;

        (d) by Parent, if (i) the board of directors of Company withdraws,
    modifies or changes its recommendation of this Agreement or the Merger in a
    manner adverse to Parent or its stockholders, (ii) the board of directors of
    Company shall have recommended to the stockholders of Company a Competing
    Transaction, (iii) the Company fails to comply in all material respects with
    Section 6.04, (iv) a Competing Transaction shall have been announced or
    otherwise publicly known and the board of directors of Company shall have
    (A) failed to recommend against acceptance of such by its stockholders
    (including by taking no position, or indicating its inability to take a
    position, with respect to the acceptance by its stockholders of a Competing
    Transaction involving a tender offer or exchange offer), (B) failed to
    reconfirm its approval and recommendation of this Agreement and the
    transactions contemplated hereby within 5 business days after Parent
    requests in writing that such recommendation be reconfirmed or
    (C) determined that such Competing Transaction was a Superior Proposal and
    takes any of the actions allowed by clause (ii) of Section 6.04, or (v) the
    board of directors of Company resolves to take any of the actions described
    above;

                                      A-34
<PAGE>
        (e) by Parent or Company, if (i) this Agreement and the Merger shall
    fail to receive the requisite votes for approval at the Company
    Stockholders' Meeting or any adjournment or postponement thereof or (ii) if
    the Share Issuance shall fail to receive the requisite votes for approval at
    the Parent Shareholders' Meeting or any adjournment or postponement thereof;

        (f) by Parent, upon a breach of any representation, warranty, covenant
    or agreement on the part of Company set forth in this Agreement, or if any
    representation or warranty of Company shall have become untrue, incomplete
    or incorrect, in either case such that the conditions set forth in Section
    8.03 would not be satisfied (a "Terminating Company Breach"); provided,
    however, that if such Terminating Company Breach is curable by Company
    through the exercise of its reasonable efforts within 20 days and for so
    long as Company continues to exercise such reasonable efforts, Parent may
    not terminate this Agreement under this Section 9.01(f); and provided,
    further that the preceding proviso shall not in any event be deemed to
    extend any date set forth in paragraph (b) of this Section 9.01; or

        (g) by Company, upon breach of any representation, warranty, covenant or
    agreement on the part of Parent set forth in this Agreement, or if any
    representation or warranty of Parent shall have become untrue, incomplete or
    incorrect, in either case such that the conditions set forth in Section 8.02
    would not be satisfied (a "Terminating Parent Breach"); provided, however,
    that if such Terminating Parent Breach is curable by Parent through the
    exercise of its reasonable efforts within 20 days and for so long as Parent
    continues to exercise such reasonable efforts, Company may not terminate
    this Agreement under this Section 9.01(g); and provided, further that the
    preceding proviso shall not in any event be deemed to extend any date set
    forth in paragraph (b) of this Section 9.01.

        (h) The right of any party hereto to terminate this Agreement pursuant
    to this Section 9.01 will remain operative and in full force and effect
    regardless of any investigation made by or on behalf of any party hereto,
    any person controlling any such party or any of their respective officers,
    directors, representatives or agents, whether prior to or after the
    execution of this Agreement.

    SECTION 9.02  Effect of Termination

    Except as provided in Section 9.05, in the event of termination of this
Agreement pursuant to Section 9.01, this Agreement shall forthwith become void,
there shall be no liability under this Agreement on the part of any party hereto
or any of its affiliates or any of its or their officers or directors, and all
rights and obligations of each party hereto shall cease; provided, however, that
nothing herein shall relieve any party hereto from liability for the willful or
intentional breach of any of its representations and warranties or the willful
or intentional breach of any of its covenants or agreements set forth in this
Agreement. No termination of this Agreement shall affect the obligation of the
parties contained in the Confidentiality Agreements, which shall survive
termination of this Agreement and remain in full force and effect in accordance
with their terms.

    SECTION 9.03  Amendment

    This Agreement may be amended by the parties hereto by action taken by or on
behalf of their respective boards of directors at any time prior to the
Effective Time; provided, however, that, after the approval of this Agreement by
the stockholders of Company, no amendment may be made that changes the amount or
type of consideration into which Company common stock will be converted pursuant
to this Agreement. This Agreement may not be amended except by an instrument in
writing signed by the parties hereto.

    SECTION 9.04  Waiver

    At any time prior to the Effective Time, any party hereto may (a) extend the
time for or waive compliance with the performance of any obligation or other act
of any other party hereto, (b) waive any inaccuracy in the representations and
warranties contained herein or in any document delivered pursuant

                                      A-35
<PAGE>
hereto and (c) waive compliance by the other party with any of the agreements or
conditions contained herein. Any such extension or waiver shall be valid if set
forth in an instrument in writing signed by the party or parties to be bound
thereby.

    SECTION 9.05  Termination Fee; Expenses

    (a) Except as set forth in this Section 9.05, all Expenses incurred in
connection with this Agreement and the Merger shall be paid by the party
incurring such Expenses, whether or not the Merger is consummated, except that
Parent and Company each shall pay one-half of all Expenses (other than
attorney's and accountant's fees and expenses) incurred solely for printing,
filing (with the SEC) and mailing the Registration Statement and the Joint Proxy
Statement and all SEC and other regulatory filing fees incurred in connection
with the Registration Statement and the Joint Proxy Statement.

    (b) In the event that (i) Parent shall terminate this Agreement pursuant to
Section 9.01(d) (other than under the circumstances described in Section
9.05(d)), or (ii) this Agreement shall be terminated (x) pursuant to Section
9.01(b) or (y) pursuant to Section 9.01(e)(i) as a result of the failure to
obtain the requisite approval of the Company stockholders and, in the case of
either (x) or (y), (A) at or prior to such termination, there shall exist or
have been proposed a Competing Transaction with respect to Company and (B)
within 12 months after such termination, Company shall enter into a definitive
agreement with respect to any Competing Transaction or any Competing Transaction
involving Company shall be consummated, then, in the case of (i), promptly after
such termination, or in the case of (ii), concurrently with the consummation of
such Competing Transaction, Company shall (subject to Section 9.05(e)) pay to
Parent an amount in cash equal to $30 million (the "Termination Fee") plus
Parent's Expenses.

    (c) In the event that Parent shall terminate this Agreement pursuant to
Section 9.01(f), then Company shall promptly reimburse Parent for Parent's
Expenses, and if, within twelve months of such termination of this Agreement,
Company shall enter into a definitive agreement with respect to any Competing
Transaction or any Competing Transaction involving Company shall be consummated
concurrently with the consummation of such Competing Transaction, then Company
shall (subject to Section 9.05(e)) pay to Parent an amount in cash equal to the
Termination Fee.

    (d) In the event that Parent shall terminate this Agreement pursuant to
Section 9.01(d)(i) and (A) prior to such termination there shall have not
existed or have been proposed a Competing Transaction with respect to Company
and (B) Robertson Stephens has withdrawn the BRS Fairness Opinion, then within
30 days after such termination, Company shall pay to Parent an amount equal to
the Termination Fee plus Parent's Expenses; provided, however, that no more than
$5,000,000 of the Termination Fee need be paid in cash, any non-cash portion of
the Termination Fee to be paid by means of the issue by Company to Parent of
that number of shares of Company Common Stock (the "Termination Shares") equal
to the quotient of the amount of such non-cash portion and $93.25. Parent and
Company agree that the provisions of Section 8 of the Option Agreement shall be
applicable to the Termination Shares as if they were issued to Parent pursuant
thereto.

    (e) In the event the Termination Fee is payable pursuant to Section
9.05(b)(ii) or Section 9.05 (c) as a result of the impending consummation of a
Competing Transaction solely described by clause (iii) of the definition of such
term, then Company need not pay the Termination Fee (or, in the case of Section
9.05(b)(ii), reimburse Parent's Expenses) if Company offers Parent, at Company's
sole discretion, either (i) the right to also enter into a license, joint
venture or other arrangement with Company on the same terms and conditions as
such Competing Transaction, subject only to terms and conditions that may be
necessary to prevent Parent from having access to data of the party with which
Company is consummating such Competing Transaction (the "JV Party") (in which
case similar terms preventing the JV Party from having access to Parent's data
must be imposed on the JV Party as part of the Competing Transaction) or (ii) a
right of first refusal to enter into a license, joint venture or other
arrangement with Company, to the exclusion of the JV Party, on the same terms
and conditions as such Competing Transaction, either of which rights must be
available for exercise by Parent for at least 15 Business days.

                                      A-36
<PAGE>
    (f) Parent and Company agree that the agreements contained in Section
9.05(b), Section 9.05(c), Section 9.05(d) or Section 9.05(e) above are an
integral part of the transaction contemplated by this Agreement and constitute
liquidated damages and not a penalty. Accordingly, if Company fails to pay to
Parent any amounts due under Section 9.05(b), Section 9.05(c), Section
9.05(d) or Section 9.05(e), Company shall pay interest on such amounts at the
prime rate of Citibank, N.A. in effect on the date such payment was required to
be made.

    (g) In the event that Company shall terminate this Agreement pursuant to
Section 9.01(g), then Parent shall promptly reimburse Company for Company's
Expenses.

    (h) Neither Company nor Parent shall be entitled to reimbursement for its
Expenses hereunder in excess of $2,500,000 in the aggregate.

                                   ARTICLE X
                               GENERAL PROVISIONS

    SECTION 10.01  Non-Survival of Representations and Warranties

    The representations and warranties in this Agreement shall terminate at the
Effective Time or upon the termination of this Agreement pursuant to Section
9.01, as the case may be. This Section 10.01 shall not limit any covenant or
agreement of the parties which by its terms contemplates performance after the
Effective Time.

    SECTION 10.02  Notices

    All notices, requests, claims, demands and other communications hereunder
shall be in writing and shall be given (and shall be deemed to have been duly
given upon receipt) by delivery in person, by telecopy or facsimile, by
registered or certified mail (postage prepaid, return receipt requested) or by a
nationally recognized courier service to the respective parties at the following
addresses (or at such other address for a party as shall be specified in a
notice given in accordance with this Section 10.02):

        (a) if to Company:

       Abacus Direct Corporation
       8774 Yates Drive
       Westminster, Colorado 80030
       Attention: W. Anthony White
       Telecopier: (212) 698-8855

        with a copy to:

       Kane Kessler, P.C.
       1350 Avenue of the Americas
       New York, New York 10019
       Attention: Robert L. Lawrence, Esq.
       Telecopier: (212) 245-3009

        (b) if to Parent or Merger Sub:

       DoubleClick Inc.
       41 Madison Avenue, 32 Floor
       New York, NY 10010
       Attention: Elizabeth Wang, General Counsel
       Telecopier: (212) 889-0029

                                      A-37
<PAGE>
        with a copy to:

       Brobeck, Phleger & Harrison LLP
       1633 Broadway, 47th Floor
       New York, NY 10019
       Attention: Alexander D. Lynch, Esq.
       Telecopier: (212) 586-7878

        and

       Brobeck, Phleger & Harrison LLP
       One Market, Spear Street Tower
       San Francisco, CA 94105
       Attention: Steve L. Camahort, Esq.
       Telecopier: (415) 442-1010

    SECTION 10.03  Severability

    If any term or other provision of this Agreement is invalid, illegal or
incapable of being enforced by any rule of Law or public policy, all other
conditions and provisions of this Agreement shall nevertheless remain in full
force and effect so long as the economic or legal substance of the Merger is not
affected in any manner materially adverse to any party. Upon such determination
that any term or other provision is invalid, illegal or incapable of being
enforced, the parties hereto shall negotiate in good faith to modify this
Agreement so as to effect the original intent of the parties as closely as
possible in a mutually acceptable manner to the fullest extent permitted by
applicable Law in order that the Merger may be consummated as originally
contemplated to the fullest extent possible.

    SECTION 10.04  Assignment; Binding Effect; Benefit

    Neither this Agreement nor any of the rights, interests or obligations
hereunder shall be assigned by any of the parties hereto (whether by operation
of Law or otherwise) without the prior written consent of the other parties
hereto. Subject to the preceding sentence, this Agreement shall be binding upon
and shall inure to the benefit of the parties hereto and their respective
successors and permitted assigns. Notwithstanding anything contained in this
Agreement to the contrary, other than Section 7.04, nothing in this Agreement,
expressed or implied, is intended to confer on any person other than the parties
hereto or their respective successors and permitted assigns any rights or
remedies under or by reason of this Agreement.

    SECTION 10.05  Incorporation of Exhibits

    The Parent Disclosure Schedule, the Company Disclosure Schedule and all
Exhibits attached hereto and referred to herein are hereby incorporated herein
and made a part of this Agreement for all purposes as if fully set forth herein.

    SECTION 10.06  Governing Law

    THIS AGREEMENT SHALL BE GOVERNED BY, AND CONSTRUED AND ENFORCED IN
ACCORDANCE WITH, THE LAWS OF THE STATE OF DELAWARE OTHER THAN CONFLICT OF LAWS
PRINCIPLES THEREOF DIRECTING THE APPLICATION OF ANY LAW OTHER THAN THAT OF
DELAWARE. COURTS WITHIN THE STATE OF DELAWARE WILL HAVE JURISDICTION OVER ALL
DISPUTES BETWEEN THE PARTIES HERETO ARISING OUT OF OR RELATING TO THIS AGREEMENT
AND THE AGREEMENTS, INSTRUMENTS AND DOCUMENTS CONTEMPLATED HEREBY. THE PARTIES
HEREBY CONSENT TO AND AGREE TO SUBMIT TO THE JURISDICTION OF SUCH COURTS. EACH
OF THE PARTIES HERETO WAIVES, AND AGREES NOT TO ASSERT IN ANY SUCH DISPUTE, TO
THE FULLEST EXTENT PERMITTED BY APPLICABLE LAW, ANY CLAIM THAT (I) SUCH PARTY IS
NOT PERSONALLY

                                      A-38
<PAGE>
SUBJECT TO THE JURISDICTION OF SUCH COURTS, (II) SUCH PARTY AND SUCH PARTY'S
PROPERTY IS IMMUNE FROM ANY LEGAL PROCESS ISSUED BY SUCH COURTS OR (III) ANY
LITIGATION COMMENCED IN SUCH COURTS IS BROUGHT IN AN INCONVENIENT FORUM.

    SECTION 10.07  Waiver of Jury Trial

    EACH PARTY HERETO HEREBY IRREVOCABLY WAIVES ALL RIGHT TO TRIAL BY JURY IN
ANY PROCEEDING (WHETHER BASED ON CONTRACT, TORT OR OTHERWISE) ARISING OUT OF OR
RELATING TO THIS AGREEMENT OR ANY TRANSACTION OR AGREEMENT CONTEMPLATED HEREBY
OR THE ACTIONS OF ANY PARTY HERETO IN THE NEGOTIATION, ADMINISTRATION,
PERFORMANCE OR ENFORCEMENT HEREOF.

    SECTION 10.08  Headings; Interpretation

    The descriptive headings contained in this Agreement are included for
convenience of reference only and shall not affect in any way the meaning or
interpretation of this Agreement. The parties have participated jointly in the
negotiation and drafting of this Agreement. In the event an ambiguity or
question of intent or interpretation arises, this Agreement shall be construed
as if drafted jointly by the parties, and no presumption or burden of proof
shall arise favoring or disfavoring any party by virtue of the authorship of any
provisions of this Agreement.

    SECTION 10.09  Counterparts

    This Agreement may be executed and delivered (including by facsimile
transmission) in one or more counterparts, and by the different parties hereto
in separate counterparts, each of which when executed and delivered shall be
deemed to be an original but all of which taken together shall constitute one
and the same agreement.

    SECTION 10.10  Entire Agreement

    This Agreement (including the Exhibits, the Parent Disclosure Schedule and
the Company Disclosure Schedule) and the Confidentiality Agreements constitute
the entire agreement among the parties with respect to the subject matter hereof
and supersede all prior agreements and understandings among the parties with
respect thereto. No addition to or modification of any provision of this
Agreement shall be binding upon any party hereto unless made in writing and
signed by all parties hereto.

                                      A-39
<PAGE>
    IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
executed as of the date first written above by their respective officers
thereunto duly authorized.

<TABLE>
<S>                                                    <C>  <C>
                                                       DOUBLECLICK INC.

                                                       By:  /s/ KEVIN J. O'CONNOR
                                                            -----------------------------------------
                                                            Name: Kevin J. O'Connor
                                                            Title: Chief Executive Officer

                                                       ABACUS DIRECT CORPORATION

                                                       By:  /s/ M. ANTHONY WHITE
                                                            -----------------------------------------
                                                            Name: M. Anthony White
                                                            Title: Chief Executive Officer

                                                       ATLANTA MERGER CORP.

                                                       By:  /s/ KEVIN J. O'CONNOR
                                                            -----------------------------------------
                                                            Name: Kevin J. O'Connor
                                                            Title: Chief Executive Officer
</TABLE>

                                      A-40
<PAGE>
                                                                      APPENDIX B

    STOCK OPTION AGREEMENT (the "Agreement"), dated as of June 13, 1999, by and
between, DoubleClick Inc., a Delaware corporation ("Parent"), and Abacus Direct
Corporation, a Delaware corporation ("Company"). Capitalized terms used herein
but not defined herein shall have the meanings set forth in the Merger Agreement
referred to below.

    WHEREAS, concurrently with the execution and delivery of this Agreement,
Company, Parent and Atlanta Merger Corp., a Delaware corporation and
wholly-owned subsidiary of Parent ("Merger Sub"), are entering into an Agreement
and Plan of Merger and Reorganization, dated as of the date hereof (the "Merger
Agreement"), pursuant to which, among other things, upon the terms and subject
to the conditions thereof, Merger Sub will be merged with and into Company (the
"Merger"), with Company continuing as the surviving corporation; and

    WHEREAS, as a condition and inducement to Parent's willingness to enter into
the Merger Agreement, Parent has required that Company agree, and Company has
agreed, to grant to Parent an option to purchase certain newly issued shares of
Company's Common Stock, par value $.001 per share ("Company Common Stock"), upon
the terms and subject to the conditions set forth herein;

    NOW, THEREFORE, in consideration of the foregoing and of the mutual
covenants and agreements set forth herein and in the Merger Agreement, the
parties hereto agree as follows:

    1.  GRANT OF OPTION.  Company hereby grants to Parent an irrevocable option
(the "Company Option") to purchase up to 1,974,516 shares (the "Company Shares")
of Company Common Stock in the manner set forth below at a price (the "Exercise
Price") of $93.25 per Company Share, payable in cash; provided, however, that
the number of shares issuable to Parent pursuant hereto and pursuant to Section
9.05(e) of the Merger Agreement shall not exceed 19.99% of the outstanding
shares of Company Common Stock.

    2.  EXERCISE OF OPTION.  (a) The Company Option may be exercised by Parent,
in whole or in part at any time or from time to time after (i) the termination
of the Merger Agreement under the conditions described in Section 9.05(b)(i) or
9.05(d) of the Merger Agreement and (ii) immediately prior to the occurrence of
any event causing the Termination Fee to become payable pursuant to Section
9.05(b)(ii) or Section 9.05 (c) of the Merger Agreement. In the event Parent
wishes to exercise the Company Option, Parent shall deliver to Company a written
notice (an "Exercise Notice") specifying the total number of Company Shares it
wishes to purchase; provided that, if prior notification to or approval of any
regulatory or antitrust agency is required in connection with such purchase,
Parent shall promptly file the required notice or application for approval,
shall promptly notify Company of such filing, and shall expeditiously process
the same and the period of time that otherwise would run pursuant to this
sentence shall run instead from the date on which any required notification
periods have expired or been terminated or such approvals have been obtained and
any requisite waiting period or periods shall have passed. Each closing of a
purchase of Company Shares (an "Option Closing") shall occur at a place, on a
date and at a time designated by Parent in an Exercise Notice delivered at least
three business days prior to the date of the Option Closing. The Company Option
shall terminate upon the earlier of: (w) the Effective Time; (x) the termination
of the Merger Agreement pursuant to Section 9.01 thereof (other than a
termination in connection with which Parent is or may be entitled to any
payments as specified in Section 9.05(b), 9.05(c) or 9.05 (d) thereof); (y) 90
days following any termination of the Merger Agreement in connection with which
Parent is entitled to a payment as specified in Section 9.05(b)(i) or
9.05(d) thereof (or if, at the expiration of such 90 day period, the Company
Option cannot be exercised by reason of any applicable judgment, decree, order,
law or regulation, twenty (20) business days after such impediment to exercise
shall have been removed or shall have become final and not subject to appeal);
or (z) 90 days following the occurrence of any event in connection with which
Parent has become entitled to payment of the Termination Fee pursuant to Section
9.05(b)(ii) of the Merger Agreement (or (I) if, at the expiration of such 90 day
period, the Company Option cannot be exercised by reason of any applicable
judgment, decree, order, law or regulation, twenty (20) business days after such
impediment to exercise shall have been removed or shall have become final and
not subject to appeal and (II) at the expiration of the
<PAGE>
12-month period following termination of the Merger Agreement described in
Section 9.05(b)(ii) or 9.05(c) if the event described therein has not occurred).

        (b) Notwithstanding any other provision of this Agreement or the Merger
    Agreement, in no event shall Parent's Total Profit (as hereinafter defined)
    exceed in the aggregate $50,000,000 and, if it otherwise would exceed such
    amount Parent, in its sole discretion, shall either (i) reduce the number of
    Company Shares subject to the Company Option, (ii) pay cash to Company,
    (iii) receive a smaller Termination Fee (as defined in Section 9.05(b)of the
    Merger Agreement), (iv) deliver to Company for cancellation Company Shares
    previously purchased by Parent or (v) any combination thereof, so that
    Parent's actually realized Total Profit shall not exceed in the aggregate
    $50,000,000 after taking into account the foregoing actions.

        (c) As used herein, the term "Total Profit" shall mean the sum of (i)
    (x)the amount (before taxes but net of reasonable and customary commissions
    paid or payable in connection with such transaction) received by Parent
    pursuant to the sale of Company Shares less (y) Parent's purchase price for
    such Company Shares, (ii) any amounts (before taxes but net of reasonable
    and customary commissions paid or payable in connection with such
    transaction) received by Parent on the transfer of the Company Option (or
    any portion thereof) to any unaffiliated Person(s) (if permitted hereunder)
    or to Company and (iii) the amount received by Parent pursuant to Section
    9.05(b), 9.05(c) and 9.05(d) of the Merger Agreement.

    3.  CONDITIONS TO CLOSING.  The obligation of Company to issue the Company
Shares to Parent hereunder is subject to the conditions that (i) all consents,
approvals, orders or authorizations of, or registrations, declarations or
filings with, any Governmental Entity or Regulatory Entity if any, required in
connection with the issuance of the Company Shares hereunder shall have been
obtained or made, as the case may be; and (ii) no preliminary or permanent
injunction or other order by any court of competent jurisdiction prohibiting or
otherwise restraining such issuance shall be in effect.

    4.  CLOSING.  At each Option Closing, (a) Company will deliver to Parent a
certificate or certificates in definitive form representing the number of
Company Shares designated by Parent in its Exercise Notice, such certificate or
certificates to be registered in the name of Parent or its designee and to bear
the legend set forth in Section 10, and (b) Parent will deliver to Company the
aggregate Exercise Price for the Company Shares so designated by wire transfer
of immediately available funds or certified check or bank check. At any Option
Closing at which Parent is exercising the Company Option in part, Parent shall
present and surrender this Agreement to Company, and Company shall deliver to
Parent an executed new agreement with the same terms as this Agreement
evidencing the right to purchase the remaining balance of the shares of Company
Common Stock purchasable hereunder.

    5.  REPRESENTATIONS AND WARRANTIES OF COMPANY.  Company represents and
warrants to Parent that (a) Company is a corporation duly organized, validly
existing and in good standing under the laws of the State of Delaware and has
the corporate power and authority to enter into this Agreement and to carry out
its obligations hereunder, (b) the execution and delivery of this Agreement by
Company and the consummation by Company of the transactions contemplated hereby
have been duly authorized by all necessary corporate action on the part of
Company and other than obtaining shareholder approval, no other corporate
proceedings on the part of Company are necessary to authorize this Agreement or
any of the transactions contemplated hereby, (c) this Agreement has been duly
executed and delivered by Company and constitutes a valid and binding obligation
of Company, enforceable against Company in accordance with its terms, except as
such enforceability may be limited by bankruptcy, insolvency, reorganization,
moratorium and other laws affecting the rights and remedies of creditors
generally and general principles of equity, (d) Company has taken all action
necessary to authorize and reserve for issuance and to permit it to issue, upon
exercise of the Company Option, and at all times from the date hereof through
the expiration of the Company Option will have reserved, that number of unissued
Company Shares that are subject to the Company Option, all of which, upon their
issuance and delivery in

                                      B-2
<PAGE>
accordance with the terms of this Agreement, will be validly issued, fully paid
and nonassessable, (e) upon delivery of the Company Shares to Parent upon the
exercise of the Company Option, Parent will acquire the Company Shares free and
clear of all liens, claims, charges, encumbrances and security interests of any
nature whatsoever except those imposed by Parent, (f) except as described in
Section 4.05 of the Merger Agreement and of the Company Disclosure Schedule, the
execution and delivery of this Agreement by Company does not, and the
performance of this Agreement by Company will not, conflict with, or result in
any violation of, or default (with or without notice or lapse of time, or both)
under, or give rise to a right of termination, cancellation or acceleration of
any obligation or the loss of a benefit under, or the creation of a lien,
pledge, security interest or other encumbrance on assets pursuant to (any such
conflict, violation, default, right of termination, cancellation or
acceleration, loss or creation, a "Violation"), (A) any provision of the Amended
and Restated Certificate of Incorporation or By-laws, each as amended, of
Company or (B) any provisions of any material mortgage, indenture, lease,
contract or other agreement, instrument, permit, concession, franchise, or
license or (C) any judgment, order, decree, statute, law, ordinance, rule or
regulation applicable to Company or its properties or assets, except in the case
of clauses (B) and (C) immediately above, for violations which would not,
individually or in the aggregate, have a Company Material Adverse Effect and
(g) except as described in Section 4.05 of the Merger Agreement and of the
Company Disclosure Schedule, the execution and delivery of this Agreement by
Company does not, and the performance of this Agreement by Company will not,
require any consent, approval, authorization or permit of, or filing with or
notification to, any Governmental Entity or Regulatory Entity.

    6.  REPRESENTATIONS AND WARRANTIES OF PARENT.  Parent represents and
warrants to Company that (a) Parent is a corporation duly organized, validly
existing and in good standing under the laws of the State of Delaware and has
the corporate power and authority to enter into this Agreement and to carry out
its obligations hereunder, (b) the execution and delivery of this Agreement by
Parent and the consummation by Parent of the transactions contemplated hereby
have been duly authorized by all necessary corporate action on the part of
Parent and no other corporate proceedings on the part of Parent are necessary to
authorize this Agreement or any of the transactions contemplated hereby, (c)
this Agreement has been duly executed and delivered by Parent and constitutes a
valid and binding obligation of Parent, enforceable against Parent in accordance
with its terms, except as such enforceability may be limited by bankruptcy and
other laws affecting the rights and remedies of creditors generally and general
principles of equity, (d) assuming that the consents, approvals, authorizations,
permits, filings and notifications referred to in subsection (e) are obtained or
made, as applicable, the execution and delivery of this Agreement by Parent does
not, and the performance of this Agreement by Parent will not, result in any
Violation pursuant to, (A) any provision of the Certificate of Incorporation or
By-laws, each as amended, of Parent, (B) any provisions of any material
mortgage, indenture, lease, contract or other agreement, instrument, permit,
concession, franchise, or license or (C) any judgment, order, decree, statute,
law, ordinance, rule or regulation applicable to Parent or its properties or
assets, except in the case of each of clauses (B) and (C) immediately, above,
for Violations which would not, individually or in the aggregate, have a Parent
Material Adverse Effect, (e) except as described in Section 5.05 of the Merger
Agreement and Section 3(a) of this Agreement, and except as may be required
under the Exchange Act, the execution and delivery of this Agreement by Parent
does not, and the performance of this Agreement by Parent will not, require any
consent, approval, authorization or permit of, or filing with or notification
to, any Governmental Entity or Regulatory Entity, (f) any Company Shares
acquired upon exercise of the Company Option will not be, and the Company Option
is not being, acquired by Parent with a view to the public distribution thereof
and Parent will not sell or otherwise dispose of such shares in violation of
applicable law or this Agreement, (g) the Company Option and any Company Shares
acquired upon exercise of the Company Option are being acquired for the account
of Parent, (h) it is an "accredited investor" as defined in Regulation D under
the Securities Act, and (i) it understands that the Company Shares may not be
sold unless such sale is registered under the Securities Act or an exemption
from such registration is available.

                                      B-3
<PAGE>
    7.  PUT.

        (a) Exercise. At any time during which the Company Option is exercisable
    hereunder (the "Repurchase Period"), upon demand by Parent, Parent shall
    have the right to sell to Company (or any successor entity thereof) and
    Company (or such successor entity) shall be obligated to repurchase from
    Parent (the "Put"), all or any portion of the Company Option, to the extent
    not previously exercised, at the price set forth in subparagraph (i) below,
    and/or all or any portion of the Company Shares purchased by Parent pursuant
    thereto, at a price set forth in subparagraph (ii) below:

           (i) the difference between the "Market/Tender Offer Price" for shares
       of Company Common Stock as of the date (the "Notice Date") notice of
       exercise of the Put is given to the other party (defined as the greater
       of (A) the price per share offered as of the Notice Date pursuant to any
       tender or exchange offer or other Takeover Proposal which was made prior
       to the Notice Date and not terminated or withdrawn as of the Notice Date
       (the "Tender Price") or (B) the average of the closing prices of shares
       of Company Common Stock on the Nasdaq National Market for the ten (10)
       trading days immediately preceding the Notice Date (the "Market Price")),
       and the Exercise Price, multiplied by the number of Company Shares
       purchasable pursuant to the Company Option (or portion thereof with
       respect to which Parent is exercising its rights under this Section 7),
       but only if the Market/Tender Offer Price is greater than the Exercise
       Price;

           (ii) the Exercise Price paid by Parent for the Company Shares
       acquired pursuant to the Company Option plus the difference between the
       Market/Tender Offer Price and the Exercise Price, but only if the
       Market/Tender Offer Price is greater than the Exercise Price, multiplied
       by the number of Company Shares so purchased;

        (b) Payment and Redelivery of Company Option or Shares. In the event
    Parent exercises its rights under this Section 7, Company shall, within ten
    business days of the Notice Date, pay the required amount (the "Repurchase
    Price") to Parent in immediately available funds and Parent shall surrender
    to Company the Company Option or the certificates evidencing the Company
    Shares purchased by Parent pursuant thereto, and Parent shall represent and
    warrant that it owns such shares and that such shares are then free and
    clear of all liens, claims, charges and encumbrances of any kind or nature
    whatsoever, other than any of the same created by Company or its affiliates.

        (c) Payment Restrictions. To the extent that Company is prohibited under
    applicable law or regulation, or as a consequence of administrative policy,
    from repurchasing the Company Option and /or Shares in full, Company shall
    immediately so notify Parent and thereafter deliver or cause to be
    delivered, from time to time, to Parent the portion of the Repurchase Price
    that it is no longer prohibited from delivering, within five business days
    after the date on which Company is no longer so prohibited; provided that,
    if Company at any time after delivery of a notice of repurchase pursuant to
    Section 7(a) is prohibited under applicable law or regulation, or as a
    consequence of administrative policy, from delivering to Parent the
    Repurchase Price in full (and Company hereby undertakes to use its
    reasonable best efforts to obtain all required regulatory and legal
    approvals and to file any required notices as promptly as practicable in
    order to accomplish such repurchase), Parent may revoke its notice of the
    Put whether in whole or to the extent of the prohibition, whereupon, in the
    latter case, Company shall promptly (1) deliver to Parent that portion of
    the Repurchase Price that Company is not prohibited from delivering and
    (2) deliver to Parent as appropriate, (A) a new Agreement evidencing the
    right of Parent to purchase that number of shares of Common Stock obtained
    by multiplying the number of shares of Common Stock for which the
    surrendered Agreement was exercisable at the time of delivery of the notice
    of repurchase by a fraction, the numerator of which is the Repurchase Price
    less the portion thereof theretofore delivered to Parent and the denominator
    of which is the Repurchase Price, and/or (B) to Parent, a certificate for
    the Company Shares it is then so prohibited from repurchasing.

                                      B-4
<PAGE>
    8.  REGISTRATION RIGHTS.

        (a) Following any exercise of the Company Option, Parent may by written
    notice (the "Registration Notice") to Company request Company to register
    under the Securities Act all or any part of the shares of Company Common
    Stock acquired pursuant to this Agreement, including any voting securities
    issued by way of dividend, distribution or otherwise in respect thereof (the
    "Restricted Shares"), beneficially owned by Parent (the "Registrable
    Securities") in order to permit the sale or other distribution of such
    Registrable Securities, including pursuant to a firm commitment underwritten
    public offering; provided, however, that any such Registration Notice must
    relate to a number of shares equal to at least 4% of the outstanding shares
    of Company Common Stock and that any rights to require registration
    hereunder shall terminate with respect to any Shares that may be sold in any
    90-day period pursuant to Rule 144 under the Securities Act. The
    Registration Notice shall include a certificate executed by Parent and its
    proposed managing underwriter, which underwriter shall be an investment
    banking firm of nationally recognized standing and reasonably acceptable to
    Company (the "Manager"), stating that Manager in good faith believes that,
    based on the then prevailing market conditions, it will be able to sell the
    Registrable Securities at a per share price equal to at least 70% of the
    Fair Market Value of such shares. For purposes of this Section 8, the term
    "Fair Market Value" shall mean the per share average of the closing sale
    prices of Company's Common Stock on the Nasdaq National Market for the
    twenty (20) trading days immediately preceding the date of the Registration
    Notice.

        (b) Company shall use commercially reasonable efforts to effect, as
    promptly as practicable, the registration under the Securities Act of the
    unpurchased Registrable Securities; provided, however, that (i) Parent shall
    not be entitled to more than two effective registration statements hereunder
    and (ii) Company will not be required to file any such registration
    statement during any period of time (not to exceed 40 days after such
    request in the case of clause (A) below or 90 days in the case of clauses
    (B) and (C) below) when (A) Company is in possession of material non-public
    information which it reasonably believes would be detrimental to be
    disclosed at such time and, based on consultation with counsel to Company,
    such information would have to be disclosed if a registration statement were
    filed at that time; (B) Company is required under the Securities Act to
    include audited financial statements for any period in such registration
    statement and such financial statements are not yet available for inclusion
    in such registration statement; or (C) Company determines, in its reasonable
    good faith judgment, that such registration would interfere with any
    financing, acquisition or other material transaction involving Company or
    any of its affiliates. If consummation of the sale of any Registrable
    Securities pursuant to a registration hereunder does not occur within 180
    days after the filing with the SEC of the initial registration statement,
    then such registration shall not be taken into account as an effective
    registration for purposes of clause (i) above. Company shall use
    commercially reasonable efforts to cause any Registrable Securities
    registered pursuant to this Section 8 to be qualified for sale under the
    securities or Blue Sky laws of such jurisdictions as Parent may reasonably
    request and shall continue such registration or qualification in effect in
    such jurisdiction; provided, however, that Company shall not be required to
    qualify to do business in, or consent to general service of process in, any
    jurisdiction by reason of this provision.

        (c) The registration rights set forth in this Section 8 are subject to
    the condition that Parent shall provide Company with such information with
    respect to Parent's Registrable Securities, the plans for the distribution
    thereof, and such other information with respect to Parent as, in the
    reasonable judgment of counsel for Company, is necessary to enable Company
    to include in such registration statement all material facts required to be
    disclosed with respect to a registration thereunder.

        (d) If Company securities of the same type as the Registrable Securities
    are then authorized for quotation or trading or listing on the New York
    Stock Exchange, the Nasdaq National Market, or any other securities exchange
    or automated quotations system, Company, upon the request of Parent, shall
    promptly file an application, if required, to authorize for quotation,
    trading or listing the shares

                                      B-5
<PAGE>
    of Registrable Securities on such exchange or system and will use its
    reasonable best efforts to obtain approval, if required, of such quotation,
    trading or listing as soon as practicable.

        (e) A registration effected under this Section 8 shall be effected at
    Company's expense, except for underwriting discounts and commissions and
    fees and expenses of counsel to Parent, and Company shall provide to the
    underwriters such documentation (including certificates, opinions of counsel
    and "comfort" letters from auditors) as are customary in connection with
    underwritten public offerings as such underwriters may reasonably require.
    In connection with any such registration, the parties agree (i) to indemnify
    each other and the underwriters in the customary manner and (ii) to enter
    into an underwriting agreement in form and substance customary for
    transactions of the type contemplated hereby with the Manager and the other
    underwriters participating in such offering.

    9.  ADJUSTMENT UPON CHANGES IN CAPITALIZATION.

        (a) In the event of any change in Company Common Stock by reason of
    stock dividends, splits, mergers (other than the Merger), recapitalizations,
    combinations, exchange of shares or the like, the type and number of shares
    or securities subject to the Company Option, and the Exercise Price per
    share, shall be adjusted appropriately, and proper provision shall be made
    in the agreements governing such transaction so that Parent shall receive,
    upon exercise of the Company Option, the number and class of shares or other
    securities or property that Parent would have received in respect of the
    Company Common Stock if the Company Option had been exercised immediately
    prior to such event or the record date therefor, as applicable. If
    additional shares of Company Common Stock are issued after the date of this
    Agreement (other than pursuant to an event described in the first sentence
    of this Section 9(a)), the number of shares of Company Common Stock subject
    to the Company Option will be adjusted so that it equals 19.99% of the
    number of shares of Company Common Stock then issued and outstanding,
    without giving effect to any shares subject to or issued pursuant to the
    Company Option.

        (b) In the event that Company shall enter in an agreement: (i) to
    consolidate with or merge into any person, other than Parent or any of its
    Subsidiaries, and shall not be the continuing or surviving corporation of
    such consolidation or merger; (ii) to permit any person, other than Parent
    or one of its subsidiaries, to merge into Company and Company shall be the
    continuing or surviving corporation, but, in connection with such merger,
    the then-outstanding shares of Company Common Stock shall be changed into or
    exchanged for stock or other securities of Company or any other person or
    cash or any other property or the outstanding shares of Company Common Stock
    immediately prior to such merger shall after such merger represent less than
    50% of the outstanding shares and share equivalents of the merged company;
    or (iii) to sell or otherwise transfer all or substantially all of its
    assets to any person, other than Parent or any of its Subsidiaries, then,
    and in each such case, the agreement governing such transaction shall make
    proper provision so that upon the consummation of any such transaction and
    upon the terms and conditions set forth herein, Parent shall receive for
    each Company Share with respect to which the Company Option has not been
    exercised an amount of consideration in the form of and equal to the per
    share amount of consideration that would be received by the holder of one
    share of Company Common Stock less the Exercise Price (and, in the event of
    an election or similar arrangement with respect to the type of consideration
    to be received by the holders of Company Common Stock, subject to the
    foregoing, proper provision shall be made so that the holder of the Company
    Option would have the same election or similar rights as would the holder of
    the number of shares of Company Common Stock for which the Company Option is
    then exercisable).

    10.  RESTRICTIVE LEGENDS.  Each certificate representing shares of Company
Common Stock issued to Parent hereunder shall, to the extent applicable, include
a legend in substantially the following form:

    THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY BE REOFFERED

                                      B-6
<PAGE>
OR SOLD ONLY IF SO REGISTERED OR IF AN EXEMPTION FROM SUCH REGISTRATION IS
AVAILABLE. SUCH SECURITIES ARE ALSO SUBJECT TO ADDITIONAL RESTRICTIONS ON
TRANSFER AS SET FORTH IN THE STOCK OPTION AGREEMENT, DATED AS OF JUNE 13, 1999,
A COPY OF WHICH MAY BE OBTAINED FROM THE ISSUER.

    11.  BINDING EFFECT; NO ASSIGNMENT.  This Agreement shall be binding upon
and inure to the benefit of the parties hereto and their respective successors
and permitted assigns. Neither this Agreement nor the rights or the obligations
of either party hereto are assignable, except by operation of law, or with the
written consent of the other party. Nothing contained in this Agreement, express
or implied, is intended to confer upon any person other than the parties hereto
and their respective permitted assigns any rights or remedies of any nature
whatsoever by reason of this Agreement. Any Restricted Shares sold by Parent in
compliance with the provisions of Section 8 shall, upon consummation of such
sale, be free of the restrictions imposed with respect to such shares by this
Agreement, and any transferee of such shares shall not be entitled to the rights
of Parent. Certificates representing shares sold in a registered public offering
pursuant to Section 8 shall not be required to bear the legend set forth in
Section 10.

    12.  SPECIFIC PERFORMANCE.  The parties recognize and agree that if for any
reason any of the provisions of this Agreement are not performed in accordance
with their specific terms or are otherwise breached, immediate and irreparable
harm or injury would be caused for which money damages would not be an adequate
remedy. Accordingly, each party agrees that, in addition to other remedies, the
other party shall be entitled to an injunction restraining any violation or
threatened violation of the provisions of this Agreement. In the event that any
action should be brought in equity to enforce the provisions of this Agreement,
neither party will allege, and each party hereby waives the defense, that there
is an adequate remedy at law.

    13.  ENTIRE AGREEMENT.  This Agreement and the Merger Agreement (including
the Company Disclosure Schedule and the Parent Disclosure Schedule relating
thereto) constitute the entire agreement among the parties with respect to the
subject matter hereof and supersede all other prior agreements and
understandings, both written and oral, among the parties or any of them with
respect to the subject matter hereof.

    14.  FURTHER ASSURANCE.  Each party will execute and deliver all such
further documents and instruments and take all such further action as may be
necessary in order to consummate the transactions contemplated hereby.

    15.  VALIDITY.  The invalidity or unenforceability of any provision of this
Agreement shall not affect the validity or enforceability of the other
provisions of this Agreement, which shall remain in full force and effect. In
the event any court or other competent authority holds any provision of this
Agreement to be null, void or unenforceable, the parties hereto shall negotiate
in good faith the execution and delivery of an amendment to this Agreement in
order, as nearly as possible, to effectuate, to the extent permitted by law, the
intent of the parties hereto with respect to such provision. Each party agrees
that, should any court or other competent authority hold any provision of this
Agreement or part hereof to be null, void or unenforceable, or order any party
to take any action inconsistent herewith, or not take any action required
herein, the other party shall not be entitled to specific performance of such
provision or part hereof or to any other remedy, including but not limited to
money damages, for breach hereof or of any other provision of this Agreement or
part hereof as the result of such holding or order.

    16.  NOTICES.  Any notice or communication required or permitted hereunder
shall be in writing and either delivered personally, telegraphed or telecopied
or sent by certified or registered mail, postage prepaid, and shall be deemed to
be given, dated and received when so delivered personally, telegraphed or
telecopied or, if mailed, five business days after the date of mailing to the
following address or telecopy number, or to such other address or addresses as
such person may subsequently designate by notice given hereunder.

                                      B-7
<PAGE>
    B. if to Parent or Merger Sub, to:

       DoubleClick Inc.
       41 Madison Avenue
       New York, NY 10010
       Attention: General Counsel
       Facsimile No.:(212) 889-0029

       with a copy to:

       Brobeck, Phleger & Harrison LLP
       1633 Broadway, 47th Floor
       New York, NY 10019
       Attention: Alexander D. Lynch, Esq.
       Facsimile No.: (212) 586-7878

       and

       Brobeck, Phleger & Harrison LLP
       Spear Street Tower
       One Market
       San Francisco, CA 94105
       Attention: Steve L. Camahort, Esq.
       Facsimile No.: (415) 442-1010

    C. if to Company, to:

       Abacus Direct Corporation
       8774 Yates Drive
       Westminster, CO 80030
       Attention: M. Anthony White
       Facsimile No.: (212) 698-8855

       with a copy to:

       Kane Kessler, P.C.
       1350 Avenue of the Americas
       New York, NY 10019
       Attention: Robert L. Lawrence, Esq.
       Facsimile No.: (212) 245-3009

    17.  GOVERNING LAW.  This Agreement shall be governed by and construed in
accordance with the laws of the State of Delaware applicable to agreements made
and to be performed entirely within such State without regard to any applicable
conflicts of law rules.

    18.  DESCRIPTIVE HEADINGS.  The descriptive headings herein are inserted for
convenience of reference only and are not intended to be part of or to affect
the meaning or interpretation of this Agreement.

    19.  COUNTERPARTS.  This Agreement may be executed in counterparts, each of
which shall be deemed to be an original, but all of which, taken together, shall
constitute one and the same instrument.

    20.  EXPENSES.  Except as otherwise expressly provided herein or in the
Merger Agreement, all costs and expenses incurred in connection with the
transactions contemplated by this Agreement shall be paid by the party incurring
such expenses.

    21.  AMENDMENTS; WAIVER.  This Agreement may be amended by the parties
hereto and the terms and conditions hereof may be waived only by an instrument
in writing signed on behalf of each of the parties hereto, or, in the case of a
waiver, by an instrument signed on behalf of the party waiving compliance.

                                      B-8
<PAGE>
    IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
executed by their respective duly authorized officers as of the date first above
written.

<TABLE>
<S>                                                    <C>  <C>
                                                       DOUBLECLICK INC.

                                                       By:            /s/ KEVIN J. O'CONNOR
                                                            -----------------------------------------
                                                                     Name: Kevin J. O'Connor
                                                                  Title: CHIEF EXECUTIVE OFFICER

                                                       ABACUS DIRECT CORPORATION

                                                       By:             /s/ M. ANTHONY WHITE
                                                            -----------------------------------------
                                                                      Name: M. Anthony White
                                                                  Title: CHIEF EXECUTIVE OFFICER
</TABLE>

                       SIGNATURE PAGE TO OPTION AGREEMENT

                                      B-9
<PAGE>
                                                                      APPENDIX C

    This STOCKHOLDER AGREEMENT (this "Agreement") is made and entered into as of
June 13, 1999 between DoubleClick, Inc., a Delaware corporation ("Parent"), and
the undersigned stockholder ("Stockholder") of Abacus Direct Corporation, a
Delaware corporation ("Company"). Capitalized terms used and not otherwise
defined herein shall have the respective meanings set forth in the Merger
Agreement described below.

                                    RECITALS

    WHEREAS, pursuant to an Agreement and Plan of Merger and Reorganization
dated as of June 13, 1999 by and among Parent, Atlanta Merger Corp., a Delaware
corporation and a wholly owned subsidiary of Parent ("Merger Sub") and Company
(such agreement as it may be amended is hereinafter referred to as the "Merger
Agreement"). Parent has agreed to acquire the outstanding securities of Company
pursuant to a statutory merger of Merger Sub with and into Company (the
"Merger"), in which each outstanding share of capital stock of Company (the
"Company Capital Stock") will be converted into shares of common stock of Parent
(the "Parent Shares") at the exchange rate set forth in the Merger Agreement
(the "Transaction");

    WHEREAS, in order to induce Parent to enter into the Merger Agreement and
consummate the Transaction, Company has agreed to use its reasonable best
efforts to cause each stockholder of Company who is an affiliate of Company to
execute and deliver to Parent a Stockholder Agreement upon the terms set forth
herein; and

    WHEREAS, Stockholder is or may become the registered and beneficial owner
(within the meaning of Rule 13d-3 of the Exchange Act) of capital stock of
Company (the "Shares").

    NOW, THEREFORE, the parties agree as follows:

    1.  TRANSFER AND ENCUMBRANCE.  Stockholder is the beneficial owner of the
Shares. The Shares constitute the only shares of capital stock and voting
securities of Company beneficially owned by Stockholder. To Stockholder's
knowledge, the Shares are, and will be at all times up until the Expiration
Date, free and clear of any liens, claims, options, charges or other
encumbrances except as disclosed on the signature page hereto. Stockholder's
principal residence or place of business is accurately set forth on the
signature page hereto.

    1.2  NEW SHARES.  Stockholder agrees that any shares of capital stock or
voting securities of Company that Stockholder purchases or with respect to which
Stockholder otherwise acquires beneficial ownership after the date of this
Agreement and prior to the Expiration Date ("New Shares") shall be subject to
the terms and conditions of this Agreement to the same extent as if they
constituted Shares.

    2.  AGREEMENT TO VOTE SHARES.  Prior to the Expiration Date, at every
meeting of the stockholders of Company at which any of the following is
considered or voted upon, and at every adjournment thereof, and on every action
or approval by written resolution of the stockholders of Company with respect to
any of the following, Stockholder shall vote the Shares and any New Shares in
favor of approval and adoption of the Merger Agreement and of the Transaction.

    3.  IRREVOCABLE PROXY.  Stockholder hereby agrees to timely deliver to
Parent a duly executed proxy in the form attached hereto as Exhibit I (the
"Proxy"), such Proxy to cover the Shares and all New Shares in respect of which
Stockholder is entitled to vote at each meeting of the stockholders of Company
(including, without limitation, each written consent in lieu of a meeting). In
the event that Stockholder is unable to provide any such Proxy in a timely
manner, Stockholder hereby grants Parent a power of attorney to execute and
deliver such Proxy for and on behalf of Stockholder, such power of attorney,
which being coupled with an interest, shall survive any death, disability,
bankruptcy, or any other such impediment of Stockholder. Upon the execution of
this Agreement by Stockholder, Stockholder hereby revokes any and all prior
proxies or powers of attorney given by Stockholder with respect to the Shares
and agrees not to grant any subsequent proxies or powers of attorney with
respect to the Shares until after the Expiration Date.
<PAGE>
    4.  REPRESENTATIONS, WARRANTIES AND COVENANTS OF STOCKHOLDER.  Stockholder
hereby represents, warrants and covenants to Parent as follows:

        (a) Stockholder has full power and legal capacity to execute and deliver
    this Agreement, to perform its obligations hereunder and to consummate the
    transactions contemplated hereby. This Agreement has been duly and validly
    executed and delivered by Stockholder and constitutes the valid and binding
    obligation of Stockholder, enforceable against Stockholder in accordance
    with its terms except as may be limited by (i) the effect of bankruptcy,
    insolvency, conservatorship, arrangement, moratorium or other laws affecting
    or relating to the rights of creditors generally, or (ii) the
    rules governing the availability of specific performance, injunctive relief
    or other equitable remedies and general principles of equity, regardless of
    whether considered in a proceeding in equity or at law. To Stockholder's
    knowledge, the execution and delivery of this Agreement by Stockholder does
    not, and the performance of Stockholder's obligations hereunder will not,
    result in any breach of or constitute a default (or an event that with
    notice or lapse of time or both would become a default) under, or give to
    others any right to terminate, amend, accelerate or cancel any right or
    obligation under, or result in the creation of any lien or encumbrance on
    any Shares or New Shares pursuant to, any note, bond, mortgage, indenture,
    contract, agreement, lease, license, permit, franchise or other instrument
    or obligation to which Stockholder is a party or by which Stockholder or the
    Shares or New Shares are or will be bound or affected.

        (b) Until the Expiration Date, Stockholder will not (and will use
    Stockholder's reasonable best efforts to cause Company, its affiliates,
    officers, directors and employees and any investment banker, attorney,
    accountant or other agent retained by Stockholder, Company or any of the
    same, not to, except to the extent otherwise permitted under Section 6.04 of
    the Merger Agreement): (i) initiate or solicit, directly or indirectly, any
    proposal, plan or offer to acquire all or any material part of the business
    or properties or capital stock of Company, whether by merger, purchase of
    assets, tender offer or otherwise, or to liquidate Company or otherwise
    distribute to the stockholders of Company all or any substantial part of the
    business, properties or capital stock of Company (each, an "Acquisition
    Proposal"); (ii) initiate, directly or indirectly, any contact with any
    person in an effort to or with a view towards soliciting any Acquisition
    Proposal; (iii) furnish information concerning Company's business,
    properties or assets to any corporation, partnership, person or other entity
    or group (other than Parent, or any associate, agent or representative of
    Parent) under any circumstances that could reasonably be expected to relate
    to an actual or potential Acquisition Proposal; or (iv) negotiate or enter
    into discussions or an agreement, directly or indirectly, with any entity or
    group with respect of any potential Acquisition Proposal. In the event
    Stockholder shall receive or become aware of any Acquisition Proposal
    subsequent to the date hereof, Stockholder shall promptly inform Parent as
    to any such matter and the details thereof to the extent possible without
    breaching any other agreement to which such Stockholder is a party or
    violating its fiduciary duties. Notwithstanding the foregoing, the
    provisions of this Section 4(b) shall not be operative for any non-executive
    director of Company for so long as such director serves on Company's board
    of directors.

        (c) Stockholder understands and agrees that if Stockholder attempts to
    transfer, vote or provide any other person with the authority to vote any of
    the Shares other than in compliance with this Agreement, Company shall not,
    and Stockholder hereby unconditionally and irrevocably instructs Company to
    not, permit any such transfer on its books and records, issue a new
    certificate representing any of the Shares or record such vote unless and
    until Stockholder shall have complied with the terms of this Agreement.

    5.  ADDITIONAL DOCUMENTS.  Stockholder hereby covenants and agrees to
execute and deliver any additional documents necessary or desirable, reasonably
necessary and desirable, to carry out the purpose and intent of this Agreement.

                                      C-2
<PAGE>
    6.  TERMINATION.  This Agreement and the Proxy delivered in connection
herewith shall terminate and shall have no further force or effect as of the
Expiration Date.

    7.  MISCELLANEOUS.

    7.1  SEVERABILITY.  If any term, provision, covenant or restriction of this
Agreement is held by a court of competent jurisdiction to be invalid, void or
unenforceable, then the remainder of the terms, provisions, covenants and
restrictions of this Agreement shall remain in full force and effect and shall
in no way be affected, impaired or invalidated.

    7.2  BINDING EFFECT AND ASSIGNMENT.  This Agreement and all of the
provisions hereof shall be binding upon and inure to the benefit of the parties
hereto and their respective successors and permitted assigns, but, except as
otherwise specifically provided herein, neither this Agreement nor any of the
rights, interests or obligations of the parties hereto may be assigned by either
of the parties without the prior written consent of the other. This Agreement is
intended to bind Stockholder solely as a securityholder of Company only with
respect to the specific matters set forth herein.

    7.3  AMENDMENT AND MODIFICATION.  This Agreement may not be modified,
amended, altered or supplemented except by the execution and delivery of a
written agreement executed by the parties hereto.

    7.4  SPECIFIC PERFORMANCE; INJUNCTIVE RELIEF.  The parties hereto
acknowledge that Parent will be irreparably harmed and that there will be no
adequate remedy at law for a violation of any of the covenants or agreements of
Stockholder set forth herein. Therefore, it is agreed that, in addition to any
other remedies that may be available to Parent upon any such violation, Parent
shall have the right to enforce such covenants and agreements by specific
performance, injunctive relief or by any other means available to Parent at law
or in equity and Stockholder hereby waives any and all defenses which could
exist in its favor in connection with such enforcement and waives any
requirement for the security or posting of any bond in connection with such
enforcement.

    7.5  NOTICES.  All notices, requests, demands or other communications that
are required or may be given pursuant to the terms of this Agreement shall be in
writing and shall be deemed to have been duly given if delivered by hand or
mailed by registered or certified mail, postage prepaid, or sent by facsimile
transmission, as follows:

        (a) If to Stockholder, at the address set forth below Stockholder's
    signature at the end hereof.

        (b) if to Parent, to:

           DoubleClick Inc.
           41 Madison Avenue
           New York, NY 10010
           Attention: General Counsel
           Facsimile No.: (212) 889-0029

           with a copy to:

           Brobeck, Phleger & Harrison LLP
           1633 Broadway, 47th Floor
           New York, NY 10019
           Attention: Alexander D. Lynch, Esq.
           Facsimile No.: (212) 581-1600
           Telephone No.: (212) 586-7878

                                      C-3
<PAGE>
           Brobeck, Phleger & Harrison LLP
           Spear Street Tower
           One Market
           San Francisco, CA 94105
           Attention: Steve L. Camahort, Esq.
           Facsimile No.: (415) 442-1010
           Telephone No.: (415) 442-0900

or to such other address as any party hereto or any Indemnified Person may
designate for itself by notice given as herein provided.

    9.6  GOVERNING LAW.  This Agreement shall be governed by, construed and
enforced in accordance with the internal laws of the State of Delaware without
giving effect to the principles of conflicts of law thereof.

    9.7  ENTIRE AGREEMENT.  This Agreement and the Proxy contain the entire
understanding of the parties in respect of the subject matter hereof, and
supersede all prior negotiations and understandings between the parties with
respect to such subject matter.

    9.8  COUNTERPART.  This Agreement may be executed in several counterparts,
each of which shall be an original, but all of which together shall constitute
one and the same agreement.

    9.9  EFFECT OF HEADINGS.  The section headings herein are for convenience
only and shall not affect the construction or interpretation of this Agreement.

                                      C-4
<PAGE>
    IN WITNESS WHEREOF, the parties have caused this Stockholder Agreement to be
executed as of the date first above written.

<TABLE>
<S>     <C>                                                    <C>
DOUBLECLICK INC.                                                            STOCKHOLDER

By:
             -------------------------------------------       -------------------------------------
                                                                            (Signature)
Name:
             -------------------------------------------

Title:
             -------------------------------------------       -------------------------------------
                                                                       (Signature of Spouse)
                                                               -------------------------------------
                                                                    (Print Name of Stockholder)

                                                               -------------------------------------
                                                                       (Print Street Address)

                                                               -------------------------------------
                                                                    (Print City, State and Zip)

                                                               -------------------------------------
                                                                      (Print Telephone Number)

                                                               -------------------------------------
                                                                (Social Security or Tax I.D. Number)
</TABLE>

                    SIGNATURE PAGE TO STOCKHOLDER AGREEMENT

                                      C-5
<PAGE>
                                                                       EXHIBIT I

                               IRREVOCABLE PROXY
                                TO VOTE STOCK OF
                           ABACUS DIRECT CORPORATION

    The undersigned stockholder of Abacus Direct Corporation, a Delaware
corporation ("Company"), hereby irrevocably (to the full extent permitted by the
Delaware General Corporation Law) appoints the members of the Board of Directors
of DoubleClick Inc., a Delaware corporation ("Parent"), and each of them, or any
other designee of Parent, as the sole and exclusive attorneys and proxies of the
undersigned, with full power of substitution and resubstitution, to vote and
exercise all voting and related rights (to the full extent that the undersigned
is entitled to do so) with respect to all of the shares of capital stock of
Company that now are or hereafter may be beneficially owned by the undersigned,
and any and all other shares or securities of Company issued or issuable in
respect thereof on or after the date hereof (collectively, the "Shares") in
accordance with the terms of this Irrevocable Proxy. Upon the undersigned's
execution of this Irrevocable Proxy, any and all prior proxies given by the
undersigned with respect to any Shares are hereby revoked and the undersigned
agrees not to grant any subsequent proxies with respect to the Shares until
after the Expiration Date (as defined below).

    This Irrevocable Proxy is irrevocable (to the extent provided in the
Delaware General Corporation Law), is coupled with an interest, including, but
not limited to, that certain Company Affiliate Agreement dated as of even date
herewith by and among Parent, and the undersigned, and is granted in
consideration of Parent entering into that certain Agreement and Plan of Merger
and Reorganization (the "Merger Agreement") by and among Parent and Atlanta
Merger Corp., a Delaware corporation and a wholly owned subsidiary of Parent
("Merger Sub"), and Company which Merger Agreement provides for the merger of
Merger Sub with and into Company (the "Merger"). As used herein, the term
"Expiration Date" shall mean the earlier to occur of (i) such date and time as
the Merger shall become effective in accordance with the terms and provisions of
the Merger Agreement, and (ii) the date of termination of the Merger Agreement.

    The attorneys and proxies named above, and each of them are hereby
authorized and empowered by the undersigned, at any time prior to the Expiration
Date, to act as the undersigned's attorney and proxy to vote the Shares, and to
exercise all voting and other similar rights of the undersigned with respect to
the Shares (including, without limitation, the power to execute and deliver
written consents pursuant to the Delaware General Corporation Law), at every
annual, special or adjourned meeting of the stockholders of Company and in every
written consent in lieu of such meeting:

       in favor of approval and adoption of the Merger Agreement and of the
       transaction contemplated thereby.

    The attorneys and proxies named above may not exercise this Irrevocable
Proxy on any other matter except as provided above. The undersigned stockholder
may vote the Shares on all other matters.

                                      C-6
<PAGE>
    All authority herein conferred shall survive the death or incapacity of the
undersigned and any obligation of the undersigned hereunder shall be binding
upon the heirs, personal representatives, successors and assigns of the
undersigned.

    This Irrevocable Proxy is coupled with an interest as aforesaid and is
irrevocable.

Dated: June 13, 1999

 -------------------------------------------------------------------------------
                                    (Signature of Stockholder)

 -------------------------------------------------------------------------------
                                    (Print Name of Stockholder)

                                    Shares beneficially owned:

                                    ___ shares of Company Common Stock

                      SIGNATURE PAGE TO IRREVOCABLE PROXY

                                      C-7
<PAGE>
                                                                      APPENDIX D

Goldman, Sachs & Co.
85 Broad Street
New York, NY 10004
Tel: 212-902-1000

PERSONAL AND CONFIDENTIAL

June 13, 1999

Board of Directors
DoubleClick Inc.
41 Madison Avenue
New York, NY 10010

Gentlemen:

    You have requested our opinion as to the fairness from a financial point of
view to DoubleClick Inc. (the "Company") of the exchange ratio of 1.05 shares of
Common Stock, par value $0.001 per share (the "Company Shares"), of the Company
to be paid for each share (the "Exchange Ratio") of Common Stock, par value
$0.001 per share (the "Abacus Shares"), of Abacus Direct Corporation ("Abacus")
pursuant to the Agreement and Plan of Merger, dated as of June 13, 1999, between
the Company, Atlanta Merger Corp., a wholly-owned subsidiary of the Company, and
Abacus (the "Agreement").

    Goldman, Sachs & Co., as part of its investment banking business, is
continually engaged in the valuation of businesses and their securities in
connection with mergers and acquisitions, negotiated underwritings, competitive
biddings, secondary distributions of listed and unlisted securities, private
placements and valuations for estate, corporate and other purposes. We are
familiar with the Company having provided certain investment banking services to
the Company from time to time, including having acted as managing underwriter of
the initial public offering of Company Shares in February 1998 and a subsequent
public offering of Company Shares in December 1998, and having acted as its
financial advisor in connection with, and having participated in certain of the
negotiations leading to, the Agreement. Goldman, Sachs & Co. provides a full
range of financial advisory and securities services and, in the course of its
normal trading activities, may from time to time effect transactions and hold
securities, including derivative securities, of the Company or Abacus for its
own account and for the accounts of customers.

    In connection with this opinion, we have reviewed, among other things, the
Agreement; the Registration Statement on Form S-1 relating to the initial public
offering of the Company Shares, including the Prospectus therein dated
February 20, 1998; Annual Reports to Stockholders and Annual Reports on
Form 10-K of Abacus and the Company for the three years and one year,
respectively, ended December 31, 1998; certain interim reports to stockholders
and Quarterly Reports on Form 10-Q of Abacus and the Company; certain other
communications from Abacus and the Company to their respective stockholders; and
certain internal financial analyses and forecasts for Abacus and the Company
prepared by their respective managements, including certain operating synergies
projected by the managements of Abacus and the Company to result from the
transaction contemplated by the Agreement. We also have held discussions with
members of the senior management of Abacus and the Company regarding the
strategic rationale for, and the potential benefits of, the transaction
contemplated by the Agreement and the past and current business operations,
financial condition and future prospects of their respective companies. In
addition, we have reviewed the reported price and trading activity for the
Abacus Shares and the Company Shares, compared certain financial and stock
market information for Abacus and the Company with similar information for
certain other companies the securities of which are publicly traded, reviewed
the financial terms of certain recent business combinations in the Internet and
direct marketing industries

                                      D-1
<PAGE>
Board of Directors
DoubleClick Inc.
June 13, 1999
Page Two

specifically and in other industries generally and performed such other studies
and analyses as we considered appropriate.

    We have relied upon the accuracy and completeness of all of the financial
and other information reviewed by us and have assumed such accuracy and
completeness for purposes of rendering this opinion. In addition, we have not
made an independent evaluation or appraisal of the assets and liabilities of
Abacus or the Company or any of their subsidiaries and we have not been
furnished with any such evaluation or appraisal. We have assumed with your
consent that the transaction contemplated by the Agreement will be accounted for
as a pooling-of-interests under generally accepted accounting principles. Our
advisory services and the opinion expressed herein are provided for the
information and assistance of the Board of Directors of the Company in
connection with its consideration of the transaction contemplated by the
Agreement and such opinion does not constitute a recommendation as to how any
holder of Company Shares should vote with respect to such transaction.

    Based upon and subject to the foregoing and based upon such other matters as
we consider relevant, it is our opinion that as of the date hereof the Exchange
Ratio pursuant to the Agreement is fair from a financial point of view to the
Company.

Very truly yours,
/s/ GOLDMAN, SACHS & CO.
- --------------------------------------

(Goldman, Sachs & Co.)

                                      D-2
<PAGE>
                                                                      APPENDIX E

BancBoston Robertson Stephens Inc.
Suite 2600
555 California Street
San Francisco, CA 94104
415-781-9700

                                                                          [LOGO]

                                 June 13, 1999

Board of Directors
Abacus Direct Corporation
11101 West 120th Avenue
Broomfield, CO 80021

Members of the Board:

    We understand that Abacus Direct Corporation ("Abacus"), DoubleClick Inc.
("DoubleClick") Atlanta Merger Corp. (a wholly owned subsidiary of DoubleClick,
"Merger Sub") are proposing to enter into an Agreement and Plan of Merger and
Reorganization (the "Agreement") which will provide, among other things, for the
merger (the "Merger") of Merger Sub with and into Abacus. Upon consummation of
the Merger, Abacus will become a wholly owned subsidiary of DoubleClick. Under
the terms set forth in a draft of the Agreement dated June 9, 1999 (the "Draft
Agreement"), at the effective time of the Merger, the outstanding shares of
common stock of Abacus, par value $.001 per share ("Abacus Common Stock"), other
than certain shares to be canceled pursuant to the Agreement, will be converted
into the right to receive 1.05 shares (the "Exchange Ratio") of the common stock
of DoubleClick, par value $.001 par share ("DoubleClick Common Stock"). The
terms and conditions of the Merger are set out more fully in the Agreement.

    You have asked us whether, in our opinion, the Exchange Ratio is fair from a
financial point of view and as of the date hereof to the "Holders of Abacus
Common Stock". The "Holders of Abacus Common Stock" shall be defined as all
holders of Abacus Common Stock other than DoubleClick, Merger Sub or any
affiliates of DoubleClick or Merger Sub.

    For purposes of this opinion we have, among other things:

    (i) reviewed certain publicly available financial statements and other
        business and financial information of Abacus and DoubleClick,
        respectively;

    (ii) reviewed certain internal financial statements and other financial and
         operating data concerning Abacus and DoubleClick prepared by the
         managements of Abacus and DoubleClick, respectively;

   (iii) reviewed certain financial forecasts and other forward looking
         financial information relating to Abacus and DoubleClick prepared by
         the managements of Abacus and DoubleClick, respectively. In addition,
         we reviewed with Abacus and DoubleClick the publicly available
         consensus estimates of research analysts relating to Abacus and
         DoubleClick, respectively;

    (iv) held discussions with the respective managements of Abacus and
         DoubleClick concerning the businesses, past and current operations,
         financial condition and future prospects of both Abacus and
         DoubleClick, independently and combined, including discussions with the
         managements of
<PAGE>
Board of Directors
Abacus Corporation
June 13, 1999
Page 2

        Abacus and DoubleClick concerning cost savings and other synergies that
        are expected to result from the Merger as well as their views regarding
        the strategic rationale for the Merger;

    (v) reviewed the financial terms and conditions set forth in the Draft
        Agreement;

    (vi) reviewed the stock price and trading history of Abacus and DoubleClick;

   (vii) compared the financial performance of Abacus and DoubleClick and the
         prices and trading activity of Abacus Common Stock and DoubleClick
         Common Stock with that of certain other publicly traded companies
         comparable with Abacus and DoubleClick, respectively;

  (viii) compared the financial terms of the Merger with the financial terms, to
         the extent publicly available, of other transactions that we deemed
         relevant;

    (ix) reviewed the pro forma impact of the Merger on DoubleClick's net
         revenue per share;

    (x) reviewed and considered in the analysis, information prepared by members
        of management of Abacus and DoubleClick relating to the relative
        contributions of Abacus and DoubleClick to the combined company;

    (xi) prepared a discounted cash flow analysis of Abacus;

   (xii) participated in discussions and negotiations among representatives of
         Abacus and DoubleClick and their financial and legal advisors; and

  (xiii) made such other studies and inquiries, and reviewed such other data, as
         we deemed relevant.

    In our review and analysis, and in arriving at our opinion, we have assumed
and relied upon the accuracy and completeness of all of the financial and other
information provided to us (including information furnished to us orally or
otherwise discussed with us by management of Abacus and DoubleClick) or publicly
available and have neither attempted to verify, nor assumed responsibility for
verifying, any of such information. We have relied upon the assurances of
management of Abacus and DoubleClick that they are not aware of any facts that
would make such information inaccurate or misleading. Furthermore, we did not
obtain or make, or assume any responsibility for obtaining or making, any
independent evaluation or appraisal of the properties, assets or liabilities
(contingent or otherwise) of Abacus or DoubleClick, nor were we furnished with
any such evaluation or appraisal. With respect to the financial forecasts and
projections (and the assumptions and bases therefor, including synergies related
to the Merger) for each of Abacus and DoubleClick that we have reviewed, upon
the advice of the managements of Abacus and DoubleClick, we have assumed that
such forecasts and projections have been reasonably prepared in good faith on
the basis of reasonable assumptions and reflect the best currently available
estimates and judgments as to the future financial condition and performance of
Abacus and DoubleClick, respectively, and we have further assumed that such
projections and forecasts (including synergies) will be realized in the amounts
and in the time periods currently estimated. In this regard, we note that each
of Abacus and DoubleClick face exposure to the Year 2000 problem. We have not
undertaken any independent analysis to evaluate the reliability or accuracy of
the assumptions made by the managements of Abacus and DoubleClick with respect
to the potential effect that the Year 2000 problem might have on their
respective forecasts. We have assumed that the Merger will be consummated upon
the terms set forth in the Draft Agreement without material alteration thereof,
including, among other things, that the Merger will be accounted for as a
"pooling-of-interests" business combination in accordance with U.S. generally
accepted accounting principles ("GAAP") and that the Merger will be treated as a
tax-free reorganization pursuant to the Internal Revenue Code of 1986, as
amended. In addition, we have assumed that the historical financial statements
of each of Abacus and DoubleClick reviewed by us have been prepared and fairly
presented in accordance with U.S. GAAP consistently applied. We have relied as
to all legal matters relevant to rendering our opinion on the advice of counsel.

                                      E-2
<PAGE>
Board of Directors
Abacus Corporation
June 13, 1999
Page 3

    This opinion is necessarily based upon market, economic and other conditions
as in effect on, and information made available to us as of, the date hereof. It
should be understood that subsequent developments may affect the conclusion
expressed in this opinion and that we disclaim any undertaking or obligation to
advise any person of any change in any matter affecting this opinion which may
come or be brought to our attention after the date of this opinion. Our opinion
is limited to the fairness, from a financial point of view and as to the date
hereof, to the Holders of Abacus Common Stock of the Exchange Ratio. We do not
express any opinion as to (i) the value of any employee agreement or other
arrangement entered into in connection with the Merger, (ii) any tax or other
consequences that might result from the Merger or (iii) what the value of
DoubleClick Common Stock will be when issued to Abacus stockholders pursuant to
the Merger or the price at which the shares of DoubleClick Common Stock that are
issued pursuant to the Merger may be traded in the future. Our opinion does not
address the relative merits of the Merger and the other business strategies that
Abacus' Board of Directors has considered or may be considering, nor does it
address the decision of the Abacus Board of Directors to proceed with the
Merger.

    We are acting as financial advisor to Abacus in connection with the Merger
and will receive (i) a fee contingent upon the delivery of this opinion and (ii)
an additional fee contingent upon the consummation of the Merger. In addition,
Abacus has agreed to indemnify us for certain liabilities that may arise out of
our engagement. In the past, we have provided certain investment banking
services to Abacus for which we have been paid fees, including acting as lead
manager for Abacus' initial public offering. We maintain a market in the shares
of Abacus Common Stock and DoubleClick Common Stock. In the ordinary course of
business, we may trade in Abacus' securities and DoubleClick's securities for
our own account and the account of our customers and, accordingly, may at any
time hold a long or short position in Abacus' securities or DoubleClick's
securities.

    Our opinion expressed herein is provided for the information of the Board of
Directors of Abacus in connection with its evaluation of the Merger. Our opinion
is not intended to be and does not constitute a recommendation to any
stockholder of Abacus or DoubleClick as to how such stockholder should vote, or
take any other action, with respect to the Merger. This opinion may not be
summarized, described or referred to or furnished to any party except with our
express prior written consent.

    Based upon and subject to the foregoing considerations, it is our opinion
that, as of the date hereof, the Exchange Ratio is fair to the Holders of Abacus
Common Stock from a financial point of view.

                                          Very truly yours,
                                          /s/ BANCBOSTON ROBERTSON STEPHENS
                                          INC.
                                          --------------------------------------
                                          BancBoston Robertson Stephens Inc.

                                      E-3
<PAGE>
                                    PART II
                     INFORMATION NOT REQUIRED IN PROSPECTUS

ITEM 20. INDEMNIFICATION OF DIRECTORS AND OFFICERS.

    The Registrant's certificate of incorporation provides that, except to the
extent prohibited by the Delaware General Corporation Law (the "DGCL"), the
Registrant's directors shall not be personally liable to the Registrant or its
stockholders for monetary damages for any breach of fiduciary duty as directors
of the Registrant. Under the DGCL, the directors have a fiduciary duty to the
Registrant which is eliminated by this provision of the certificate of
incorporation and, in appropriate circumstances, equitable remedies such as
injunctive or other forms of nonmonetary relief will remain available. In
addition, each director will continue to be subject to liability under the DGCL
for breach of the director's duty of loyalty to the Registrant, for acts or
omissions which are found by a court of competent jurisdiction to be not in good
faith or involving intentional misconduct, for knowing violations of law, for
actions leading to improper personal benefit to the director, and for payment of
dividends or approval of stock repurchases or redemptions that are prohibited by
the DGCL. This provision also does not affect the directors' responsibilities
under any other laws, such as the federal securities laws or state or federal
environmental laws. The Registrant has obtained liability insurance for its
officers and directors.

    Section 145 of the DGCL empowers a corporation to indemnify its directors
and officers and to purchase insurance with respect to liability arising out of
their capacity or status as directors and officers, provided that this provision
shall not eliminate or limit the liability of the director: (i) for any breach
of the director's duty of loyalty to the corporation or its stockholders,
(ii) for acts or omissions not in good faith or which involve intentional
misconduct or a knowing violation of law, (iii) arising under Section 174 of the
DGCL, or (iv) for any transaction from which the director derived an improper
personal benefit. The DGCL provides further that the indemnification permitted
thereunder shall not be deemed exclusive of any other rights to which the
directors and officers may be entitled under the corporation's certificate of
incorporation or bylaws, any agreement, a vote of stockholders or otherwise. The
Registrant's certificate of incorporation eliminates the personal liability of
directors to the fullest extent permitted by the DGCL and provides that the
Registrant shall fully indemnify any person who was or is a party or is
threatened to be made a party to, any threatened, pending or completed action,
suite or proceeding (whether civil, criminal, administrative of investigative)
by reason of the fact that such person is or was a director or officer of the
Registrant, or is or was serving at the request of the Registrant as a director
or officer of another corporation, partnership, joint venture, trust, employee
benefit plan or other enterprise, against expenses (including attorney's fees),
judgments, fines and amounts paid in settlement actually and reasonably incurred
by such person in connection with such action, suit or proceeding.

    At present, there is no pending litigation or proceeding involving any
director, officer, employee or agent as to which indemnification will be
required or permitted under the Registrant's certificate of incorporation. The
Registrant is not aware of any threatened litigation or proceeding that may
result in a claim for such indemnification.

ITEM 21. EXHIBITS AND FINANCIAL STATEMENT SCHEDULES.

    (a) EXHIBITS

    The following is a list of Exhibits filed as part of the Registration
Statement or incorporated by reference herein:

<TABLE>
<CAPTION>
       EXHIBIT
       NUMBER                                   DESCRIPTION
- ---------------------   ------------------------------------------------------------
<C>                     <S>
          2.1           Agreement and Plan of Merger and Reorganization dated as of
                        June 13, 1999, by and among the Registrant, Atlanta Merger
                        Corp. and Abacus Direct Corporation (attached as Appendix A
                        to the joint proxy statement/prospectus contained in this
                        registration statement).
</TABLE>

                                      II-1
<PAGE>

<TABLE>
<CAPTION>
       EXHIBIT
       NUMBER                                   DESCRIPTION
- ---------------------   ------------------------------------------------------------
<C>                     <S>
          3.1           Registrant's Amended and Restated Certificate of
                        Incorporation (incorporated by reference to Exhibit 3.1 of
                        the Registrant's Registration Statement on Form S-1 (File
                        No. 333-67459)).
          3.2           Registrant's Amended and Restated Bylaws (incorporated by
                        reference to Exhibit 3.5 of the Registrant's Registration
                        Statement on Form S-1 (File No. 333-42323)).
          4.1           Indenture, dated as of March 22, 1999, between the
                        Registrant and the Bank of New York, as trustee, including
                        the form of 4.75% Convertible Subordinated Notes due 2006
                        attached as Exhibit A thereto (incorporated by reference to
                        Exhibit 6.1 of the Registrant's Quarterly Report on Form
                        10-Q for the quarter ended March 31, 1999).
          4.2           Registration Agreement, dated as of March 22, 1999, by and
                        among The Registrant and the Initial Purchasers
                        (incorporated by reference to Exhibit 6.2 of The
                        Registrant's Quarterly Report on Form 10-Q for the quarter
                        ended March 31, 1999).
          5.1           Opinion of Brobeck, Phleger & Harrison LLP regarding the
                        legality of the securities being issued.
          8.1           Opinion of Parker Chapin Flattau & Klimpl LLP regarding
                        certain tax matters.
         10.1           Proposed DoubleClick Inc. Employee Stock Purchase Plan.
         23.1           Consent of Brobeck, Phleger & Harrison, included in Exhibit
                        5.1.
         23.2           Consent of Parker Chapin Flattau & Klimpl LLP, included in
                        Exhibit 8.1.
         23.3           Consent of PricewaterhouseCoopers LLP.
         23.4           Consent of PricewaterhouseCoopers LLP.
         23.5           Consent of KPMG LLP.
         23.6           Consent of Goldman, Sachs & Co.
         23.7           Consent of BancBoston Robertson Stephens Inc.
         24.1           Power of Attorney, included on the signature page of this
                        Registration Statement.
         99.1           Form of DoubleClick Proxy Card.
         99.2           Form of Abacus Proxy Card.
</TABLE>

                                      II-2
<PAGE>
        (b) FINANCIAL STATEMENT SCHEDULES

        None.

        (c) Opinion of Goldman, Sachs & Co., attached as Annex D to the joint
    proxy statement/ prospectus which is part of this registration statement.
    Opinion of BancBoston Robertson Stephens Inc., attached as Annex E to the
    joint proxy statement/prospectus which is part of this registration
    statement.

ITEM 22. UNDERTAKINGS

    The undersigned Registrant hereby undertakes:

    (1)  To file, during any period in which offers or sales are being made, a
post effective amendment to this registration statement:

    (i) To include any prospectus required by Section 10(a)(3) of the Securities
        Act of 1933;

    (ii) To reflect in the prospectus any facts or events arising after the
         effective date of the registration statement (or the most recent
         post-effective amendment thereof) which, individually or in the
         aggregate, represent a fundamental change in the information set forth
         in the registration statement. Notwithstanding the foregoing, any
         increase or decrease in volume of securities offered (if the total
         dollar value of securities offered would not exceed that which was
         registered) and any deviation from the low or high end of the estimated
         maximum offering range may be reflected in the form of prospectus filed
         with the Commission pursuant to Rule 424(b) if, in the aggregate, the
         changes in volume and price represent no more than 20 percent change in
         the maximum aggregate offering price set forth in the "Calculation of
         Registration Fee" table in the effective registration statement;

   (iii) To include any material information with respect to the plan of
         distribution not previously disclosed in the registration statement or
         any material change to such information in the registration statement;

    (2)  That, for the purpose of determining any liability under the Securities
Act of 1933, each such post effective amendment shall be deemed to be a new
registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial BONA
FIDE offering thereof;

    (3)  To remove from registration by means of a post-effective amendment any
of the securities being registered which remain unsold at the termination of the
offering;

    (4)  that, for purposes of determining any liability under the Securities
Act of 1933, each filing of the Registrant's annual report pursuant to
Section 13(a) or Section 15(d) of the Securities Exchange Act of 1934, as
amended (the "Exchange Act") that is incorporated by reference in the
registration statement shall be deemed to be a new registration statement
relating to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial BONA FIDE offering thereof;

    (5)  that, prior to any public reoffering of the securities registered
hereunder through use of a prospectus which is a part of this Registration
Statement, by any person or party who is deemed to be an underwriter within the
meaning of Rule 145(c) of the Securities Act, such reoffering prospectus will
contain the information called for by the applicable registration form with
respect to reofferings by persons who may be deemed underwriters, in addition to
the information called for by the other items of the applicable form;

    (6)  that every prospectus (i) that is filed pursuant to paragraph (2)
immediately preceding, or (ii) that purports to meet the requirements of
Section 10(a)(3) of the Securities Act and is used in connection with an
offering of securities subject to Rule 415, will be filed as a part of an
amendment to this

                                      II-3
<PAGE>
Registration Statement and will not be used until such amendment is effective,
and that, for purposes of determining any liability under the Securities Act,
each such post-effective amendment shall be deemed to be a new registration
statement relating to the securities offered therein, and the offering of such
securities at that time shall be deemed to be the initial BONA FIDE offering
thereof;

    (7)  to respond to requests for information that is incorporated by
reference into the prospectus pursuant to Item 4, 10(b), 11 or 13 of Form S-4,
within one business day of receipt of such request, and to send the incorporated
documents by first class mail or other equally prompt means. This includes
information contained in documents filed subsequent to the effective date of
this Registration Statement through the date of responding to the request; and

    (8)  to supply by means of a post-effective amendment all information
concerning a transaction, and the company being acquired involved therein, that
was not the subject of and included in this Registration Statement when it
became effective.

    Insofar as indemnification for liabilities arising under the Securities Act
of 1933 may be permitted to directors, officers and controlling persons of the
Registrant pursuant to the provisions described in Item 20 above, or otherwise,
the Registrant has been advised that in the opinion of the Securities and
Exchange Commission such indemnification is against public policy as expressed
in the Securities Act, and is, therefore, unenforceable. In the event that a
claim for indemnification against such liabilities (other than payment by the
Registrant of expenses incurred or paid by a director, officer or controlling
person of the Registrant in the successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, the Registrant will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question whether such
indemnification by it is against public policy as expressed in the Act and will
be governed by the final adjudication of such issue.

                                      II-4
<PAGE>
                                   SIGNATURES

    Pursuant to the requirements of the Securities Act of 1933, as amended, the
Registrant has duly caused this Registration Statement to be signed on its
behalf by the undersigned, thereunto duly authorized in The City of New York,
State of New York, on this 20th day of October, 1999.

<TABLE>
<S>                                                    <C>  <C>
                                                       DOUBLECLICK INC.

                                                       By:            /s/ KEVIN J. O'CONNOR
                                                            -----------------------------------------
                                                                        Kevin J. O'Connor
                                                                     CHIEF EXECUTIVE OFFICER
</TABLE>

                               POWER OF ATTORNEY

    We, the undersigned directors and/or officers of DoubleClick Inc. (the
"Company"), hereby severally constitute and appoint Kevin J. O'Connor, Chief
Executive Officer, and Stephen E. Collins, Chief Financial Officer, and each of
them individually, with full powers of substitution and resubstitution, our true
and lawful attorneys, with full powers to them and each of them to sign for us,
in our names and in the capacities indicated below, the Registration Statement
on Form S-4 filed with the Securities and Exchange Commission, and any and all
amendments to said Registration Statement (including post-effective amendments),
and any registration statement filed pursuant to Rule 462(b) under the
Securities Act of 1933, as amended, in connection with the registration under
the Securities Act of 1933, as amended, of equity securities of the Company, and
to file or cause to be filed the same, with all exhibits thereto and other
documents in connection therewith, with the Securities and Exchange Commission,
granting unto said attorneys, and each of them, full power and authority to do
and perform each and purposes as each and every act and thing requisite and
necessary to be done in connection therewith, as fully to all intents and
purposes as each of them might or could do in person, and hereby ratifying and
confirming all that said attorneys, and each of them, or their substitute or
substitutes, shall do or cause to be done by virtue of this Power of Attorney.

                                      II-5
<PAGE>
    Pursuant to the requirements of the Securities Act of 1933, as amended, this
Registration Statement to be signed by the following persons in the capacities
indicated on October 20, 1999:

<TABLE>
<CAPTION>
                        NAME                                               TITLE
                        ----                                               -----
<C>                                                    <S>
                /s/ KEVIN J. O'CONNOR                  Chief Executive Officer and Chairman of the
     -------------------------------------------         Board of Directors (Principal Executive
                  Kevin J. O'Connor                      Officer)

               /s/ STEPHEN R. COLLINS
     -------------------------------------------       Chief Financial Officer (Principal Financial
                 Stephen R. Collins                      and Accounting Officer)

     -------------------------------------------       Chief Technology Officer and Director
                 Dwight A. Merriman

                 /s/ DAVID N. STROHM
     -------------------------------------------       Director
                   David N. Strohm

                /s/ MARK E. NUNNELLY
     -------------------------------------------       Director
                  Mark E. Nunnelly

                /s/ W. GRANT GREGORY
     -------------------------------------------       Director
                  W. Grant Gregory

                 /s/ DONALD PEPPERS
     -------------------------------------------       Director
                   Donald Peppers

                /s/ THOMAS S. MURPHY
     -------------------------------------------       Director
                  Thomas S. Murphy
</TABLE>

                                      II-6
<PAGE>
                                 EXHIBIT INDEX

<TABLE>
<CAPTION>
       EXHIBIT
       NUMBER                                   DESCRIPTION
- ---------------------   ------------------------------------------------------------
<C>                     <S>
          2.1           Agreement and Plan of Merger and Reorganization dated as of
                        June 13, 1999, by and among the Registrant, Atlanta Merger
                        Corp. and Abacus Direct Corporation (attached as Appendix A
                        to the proxy statement/prospectus contained in this
                        registration statement).

          3.1           Registrant's Amended and Restated Certificate of
                        Incorporation (incorporated by reference to Exhibit 3.1 of
                        the Registrant's Registration Statement on Form S-1 (File
                        No. 333-67459)).

          3.2           Registrant's Amended and Restated Bylaws (incorporated by
                        reference to Exhibit 3.5 of the Registrant's Registration
                        Statement on Form S-1 (File No. 333-42323)).

          4.1           Indenture, dated as of March 22, 1999, between the
                        Registrant and the Bank of New York, as trustee, including
                        the form of 4.75% Convertible Subordinated Notes due 2006
                        attached as Exhibit A thereto (incorporated by reference to
                        Exhibit 6.1 of the Registrant's Quarterly Report on Form
                        10-Q for the quarter ended March 31, 1999).

          4.2           Registration Agreement, dated as of March 22, 1999, by and
                        among The Registrant and the Initial Purchasers
                        (incorporated by reference to Exhibit 6.2 of The
                        Registrant's Quarterly Report on Form 10-Q for the quarter
                        ended March 31, 1999).

          5.1           Opinion of Brobeck, Phleger & Harrison LLP regarding the
                        legality of the securities being issued.

          8.1           Opinion of Parker Chapin Flattau & Klimpl LLP regarding
                        certain tax matters.

         10.1           Proposed DoubleClick Inc. Employee Stock Purchase Plan.

         23.1           Consent of Brobeck, Phleger & Harrison, included in Exhibit
                        5.1.

         23.2           Consent of Parker Chapin Flattau & Klimpl LLP, included in
                        Exhibit 8.1.

         23.3           Consent of PricewaterhouseCoopers LLP.

         23.4           Consent of PricewaterhouseCoopers LLP.

         23.5           Consent of KPMG LLP.

         23.6           Consent of Goldman, Sachs & Co.

         23.7           Consent of BancBoston Robertson Stephens Inc.

         24.1           Power of Attorney, included on the signature page of this
                        Registration Statement.

         99.1           Form of DoubleClick Proxy Card.

         99.2           Form of Abacus Proxy Card.
</TABLE>

<PAGE>
                                                                     EXHIBIT 5.1

                                October 21, 1999

DoubleClick Inc.
41 Madison Avenue, 32nd Floor
New York, NY 10010

    Re: DoubleClick Inc. Registration Statement on Form S-4 for Issuance of
       Shares of Common Stock

Ladies and Gentlemen:

    We have acted as counsel to DoubleClick Inc., a Delaware corporation (the
"Company"), in connection with the proposed public offering of the Company's
Common Stock (the "Shares"), as described in the Company's Registration
Statement on Form S-4 (the "Registration Statement") filed on the date hereof
with the Securities and Exchange Commission under the Securities Act of 1933, as
amended (the "Act").

    This opinion is being furnished in accordance with the requirements of Item
21(a) of Form S-4 and Item 601(b)(5)(i) of Regulation S-K.

    We have reviewed the Company's charter documents, the corporate proceedings
taken by the Company in connection with the issuance and sale of the Share and
such other instruments, documents or other information as we deemed necessary or
appropriate in rendering our opinion. Based on such review, we are of the
opinion that the Shares have been duly authorized and if, as and when issued in
accordance with the Registration Statement and the related joint proxy
statement/prospectus (as amended and supplemented through the date of issuance)
will be legally issued, fully paid and nonassessable.

    We consent to the filing of this opinion as Exhibit 5.1 to the Registration
Statement and to the reference to this firm under the caption "Legal Matters" in
the prospectus which is part of the Registration Statement. In giving this
consent, we do not thereby admit that we are within the category of persons
whose consent is required under Section 7 of the Act, the rules and regulations
of the Securities and Exchange Commission promulgated thereunder, or Item 509 of
Regulation S-K.

    This opinion letter is rendered as of the date first above written and we
disclaim any obligation to advise you of facts, circumstances, events or
developments which hereafter may be brought to our attention and which may
alter, affect or modify the opinion expressed herein. Our opinion is expressly
limited to the matters set forth above and we render no opinion, whether by
implication or otherwise, as to any other matters relating to the Company or the
Shares.

                                          Very truly yours,
                                          /s/ BROBECK, PHLEGER & HARRISON LLP
                                          BROBECK, PHLEGER & HARRISON LLP

<PAGE>
                                                                     EXHIBIT 8.1

                  [PARKER CHAPIN FLATTAU & KLIMPL, LLP LETTERHEAD]

                                October 20, 1999

Abacus Direct Corporation
11101 West 120th Street
Broomfield, Colorado 80021

Ladies and Gentlemen:

    We have acted as special tax counsel for Abacus Direct Corporation
("Abacus"), a Delaware corporation, solely in connection with the Agreement and
Plan of Merger dated as of June 13, 1999, (the "Agreement") by and among
DoubleClick Inc. ("DoubleClick"), a Delaware corporation, Atlanta Merger
Corporation ("Sub"), a Delaware corporation wholly owned by DoubleClick, and
Abacus. Pursuant to the Agreement, Sub will merge with and into Abacus (the
"Merger"), and Abacus will become a wholly owned subsidiary of DoubleClick.
Except as otherwise provided, capitalized terms referred to herein have the
meanings set forth in the Agreement. All section references, unless otherwise
indicated, are to the Internal Revenue Code of 1986, as amended (the "Code").

    You have requested our opinion regarding certain United States federal
income tax consequences of the Merger. In delivering this opinion, we have
reviewed and are relying (or will rely) upon (without any independent
investigation) the truth and accuracy, at all relevant times, of the statements,
descriptions, representations and warranties contained in the Agreement
(including all schedules and exhibits thereto), the registration statement on
Form S-4 filed with the Securities and Exchange Commission (which includes a
proxy statement-prospectus relating to the Merger) (the "Registration
Statement"), certain representations and warranties set forth in certificates
provided to us by Abacus and by DoubleClick and Sub (the "Officers'
Certificates"), copies of which are attached hereto as Exhibits A and B.

    In addition, we have assumed or obtained representations and are relying
thereon (without any independent investigation or review thereof) that:

        1. Original documents (including signatures) are authentic, documents
    submitted to us as copies conform to the original documents, and there has
    been (or will be by the Effective Time) due execution and delivery of all
    documents where due execution and delivery are prerequisites to
    effectiveness thereof.

        2. The Merger will be consummated in accordance with the Agreement
    (without any waiver, breach or amendment of any of the provisions thereof)
    and will be effective under the laws of the State of Delaware. The
    representations and warranties set forth in the Agreement and the Officers'
    Certificates are and will be true, correct and complete as if made at the
    Effective Time.

        3. All statements, descriptions and representations contained in any of
    the documents referred to herein or otherwise made to us were true, correct
    and complete when made and are and will continue to be true, correct and
    complete through the Effective Time, including, but not limited to, the
    facts relating to the merger of Sub with and into Abacus as described in the
    Registration Statement, the representations set forth and documents
    described in the Registration Statement, and the business reasons for the
    Merger as set forth in the Registration Statement. No actions have been (or
    will be) taken which are inconsistent with the foregoing sentence.

        4. DoubleClick and Abacus will report the Merger on their respective
    federal income tax returns in a manner consistent with the opinion set forth
    below.

        5. Any statement or representation made "to the knowledge of" or
    otherwise similarly qualified is correct without such qualification. As to
    all matters in which a person or entity making a representation has
    represented that such person or entity either is not a party to, does not
    have, or is
<PAGE>
    not aware of any plan, intention, understanding or agreement to take an
    action, there is in fact no plan, intent, understanding or agreement and
    such action will not be taken.

        6. The terms of the Agreement and all other agreements entered into in
    connection therewith are the product of negotiations between unrelated
    parties negotiating at arm's length without duress or hardship.

    Based on our examination of the foregoing items and subject to the
assumptions, exceptions, limitations and qualifications set forth herein and in
the Registration Statement, we are of the opinion that:

        A. The Merger will constitute a reorganization within the meaning of the
    Code.

        B. A holder (the "Holder") of Abacus common stock will not recognize any
    gain or loss solely upon such Holder's receipt of DoubleClick common stock
    in exchange for such Holder's Abacus common stock in the Merger, except to
    the extent the Holder receives cash in lieu of a fractional share of
    DoubleClick common stock.

        C. The aggregate tax basis of the DoubleClick common stock that a Holder
    receives in the Merger will be the same as the aggregate tax basis of the
    Abacus common stock surrendered by such Holder in exchange for such
    DoubleClick common stock (reduced by any tax basis attributable to
    fractional shares the Holder is deemed to have disposed of).

        D. The holding period of the DoubleClick common stock that each Holder
    receives in the Merger will include the period for which the Abacus common
    stock surrendered in exchange for DoubleClick common stock was considered to
    be held, if the surrendered Abacus common stock is held as a capital asset
    at the time of the Merger,.

        E. Cash payments that a Holder receives in lieu of a fractional share
    will be treated as if the fractional share of DoubleClick common stock had
    been issued in the Merger and then redeemed by DoubleClick. A Holder
    receiving cash will recognize gain or loss upon payment measured by any
    difference between the amount of cash received and the Holder's basis in the
    fractional share.

    No opinion is expressed as to any transaction other than the Merger as
described in the Agreement or to any transaction whatsoever (including the
Merger) if all the transactions described in the Agreement are not consummated
in accordance with the terms of the Agreement and without amendment, waiver or
breach of any material provision thereof, or if any of the descriptions,
representations, warranties, statements and assumptions upon which we relied are
not true and accurate at all relevant times. In the event any one of the
descriptions, statements, representations, warranties or assumptions upon which
we have relied to issue this opinion is incorrect, our opinion might be
adversely affected and may not be relied upon.

    This opinion letter addresses only the U.S. federal income tax consequences
to a U.S. person holding common stock of Abacus as a capital asset within the
meaning of Code Section 1221. This opinion letter does not address any other
federal, state, local or foreign tax consequences that may result from the
Merger or any other transaction (including any other transaction undertaken in
connection with the Merger or in contemplation of the Merger). In particular, we
express no opinion regarding (1) whether and the extent to which any Abacus
shareholder that has provided or will provide services to Abacus, DoubleClick or
Sub will have compensation income under any provision of the Code; (2) the
effects of any such compensation income, including but not limited to the effect
upon the basis and holding period of the DoubleClick stock received by any such
shareholder in the Merger; (3) other than the fact that the Merger will be a
reorganization within the meaning of Code Section 368(a), the corporate level
tax consequences of the Merger to DoubleClick, Sub or Abacus, including without
limitation the survival and/or availability, after the Merger, of any of the
federal income tax attributes or elections of DoubleClick, Sub or Abacus or the
application of the "golden parachute" rules under Code Section 280G, after
application of any

                                       2
<PAGE>
provision of the Code, as well as the regulations promulgated thereunder and
judicial interpretations thereof; (4) the tax consequences of the Merger to
holders of options, warrants or other rights to acquire Abacus stock; and
(5) the tax consequences of the Merger as applied to specific shareholders of
Abacus or that may be relevant to particular classes of Abacus shareholders such
as dealers in securities, corporate shareholders subject to the alternative
minimum tax, foreign persons, tax-exempt organizations, banks, insurance
companies or holders of shares acquired upon exercise of stock options or in
other compensatory transactions.

    This opinion letter represents and is based upon our best judgment regarding
the application of federal income tax statutes, existing judicial decisions,
administrative regulations and published rulings and procedures in effect on the
date hereof. Our opinion is not binding upon the Internal Revenue Service or the
courts, and there is no assurance that the Internal Revenue Service will not
successfully assert a contrary position. Furthermore, no assurance can be given
that future legislative, judicial or administrative changes, on either a
prospective or retroactive basis, would not adversely affect the accuracy of the
conclusions stated herein. Nevertheless, we undertake no responsibility to
advise you of any new developments in the application or interpretation of the
federal income tax laws.

    We consent to the use of this opinion as an exhibit to the Registration
Statement, to references to this opinion in the Registration Statement and to
the use of our name in the Registration Statement under the heading "Material
Federal Income Tax Consequences." In giving this consent we do not admit that we
are within the category of persons whose consent is required under Section 7 of
the Securities Act of 1933, as amended, or the rules or regulations promulgated
thereunder.

                                          Very truly yours,
                                          /S/ PARKER CHAPIN FLATTAU & KLIMPL,
                                          LLP

                                          PARKER CHAPIN FLATTAU & KLIMPL, LLP

                                       3
<PAGE>
                                                                       EXHIBIT A

                           [DOUBLECLICK INC. LETTERHEAD]

Parker Chapin Flattau & Klimpl, LLP
1211 Avenue of the Americas                                     October 20, 1999
New York, New York 10036

    Re: TAX REPRESENTATIONS FOR REVERSE TRIANGULAR MERGER

Dear Sir:

    This letter is being furnished in connection with the merger (the "Merger")
of Atlanta Merger Corp. ("Subsidiary"), a Delaware corporation and a
wholly-owned subsidiary of DoubleClick Inc. ("Parent"), a Delaware corporation,
with and into Abacus Direct Corporation ("Company"), a Delaware corporation, in
exchange for shares of voting common stock, $0.001 par value per share, of
Parent ("Parent Common Stock") pursuant to the Agreement and Plan of Merger (the
"Merger Agreement") dated as of June 13, 1999 among Parent, Subsidiary, and
Company.(1)

    In connection with the above, Parent represents and warrants as follows:

        1.  The fair market value of the Parent Common Stock and other
    consideration received by each Company stockholder in the Merger is
    approximately equal to the fair market value of the Company stock
    surrendered by each Company stockholder in the Merger.

        2.  At least 50 percent of the aggregate value of all Company stock
    outstanding immediately prior to the Merger is preserved in the Merger
    within the meaning of Treas. Reg. Section1.368-1(e). For purposes of this
    representation, the value of a share of Company stock is considered to be
    preserved in the Merger if the share of Company stock is exchanged for
    Parent Common Stock in the Merger. However, the value of a share of Company
    stock is not preserved in the Merger (and is treated as outstanding
    immediately prior to the Merger) if and to the extent that (a) in connection
    with the Merger, the share of Company stock is acquired by Parent or a
    person related to Parent for consideration other than the Parent Common
    Stock, (b) if, prior to the Merger, the share of Company stock was redeemed
    by Company or acquired by a person related to Company, (c) if, in connection
    with the Merger, the Parent Common Stock issued in the Merger is redeemed or
    acquired by a person related to Parent, or (d) to the extent that prior to
    and in connection with the Merger, an extraordinary distribution (as such
    term is used in Treas. Reg. Section1.368-1T(e)) is made with respect to the
    share of Company stock. For purposes of this representation, persons are
    considered related if they are related within the meaning of Treas. Reg.
    Section1.369-1(e)(3).

        3.  Following the Merger, Company will hold (a) at least 90% of the fair
    market value of its net assets and at least 70% of the fair market value of
    its gross assets held immediately prior to the Merger, and (b) at least 90%
    of the fair market value of Subsidiary's net assets and at least 70% of the
    fair market value of Subsidiary's gross assets held immediately prior to the
    Merger. For purposes of the preceding sentence, amounts paid to the Company
    stockholders who receive cash or other property (including cash for
    fractional shares), amounts used by Company or Subsidiary to pay
    reorganization expenses, all redemptions and distributions (except for
    regular, normal dividends) made by Company and all assets disposed of by
    Company in contemplation of the Merger (except in the ordinary course of
    business) will be included in the assets of Company or Subsidiary, as the
    case may be, immediately prior to the Merger.

        4.  Prior to the Merger, Parent will be in Control of Subsidiary. As
    used herein, "Control" of a corporation means control as defined by IRC
    Section368(c) which defines control generally to mean ownership of stock
    possessing at least 80% of the total combined voting power of all classes of
    stock

- ------------------------
(1)  Unless otherwise noted herein, all section references are to the Internal
     Revenue Code of 1986 ("IRC") and to the regulations ("Treas. Reg.")
     promulgated thereunder, as either may be amended or otherwise modified.
<PAGE>
    entitled to vote and at least eighty 80% of the total number of shares of
    all other classes of stock of the corporation. For purposes of determining
    Control, a person will not be considered to own voting stock if rights to
    vote such stock (or to restrict or otherwise control the voting of such
    stock) are held by a third party (including a voting trust) other than an
    agent of such person.

        5.  To the best of Parent's knowledge, Company has no present plan or
    intention to issue additional shares of its stock that would result in
    Parent's losing Control of Company.

        6.  Parent has no present plan or intention to reacquire, or to cause
    any corporation related to Parent to acquire, any Parent Common Stock
    following the Merger, and no corporation related to Parent has a present
    plan or intention to purchase any Parent Common Stock. For purposes of the
    preceding sentence, persons are considered related if such persons are
    related within the meaning of Treas. Reg. Section1.368-1(e)(3). To the best
    of Parent's knowledge, neither Company nor any person related to Company has
    redeemed or acquired, nor does Company or any person related to Company have
    any plan or intention to redeem or acquire, any shares of Company stock or
    make an extraordinary distribution with respect to any shares of Company
    stock. For purposes of the preceding sentence, persons are considered
    related if such persons are related within the meaning of Treas. Reg.
    Section1.368-1T(e)(2)(ii).

        7.  Except as described in the Registration Statement (as defined in
    paragraph 24 below), Parent has no present plan or intention to otherwise
    (a) liquidate Company; (b) merge Company with or into another corporation;
    (c) sell, distribute or otherwise dispose of Company capital stock;
    (d) cause Company to sell or otherwise dispose of any of its assets (or any
    assets acquired from Subsidiary), except for dispositions made in the
    ordinary course of business, transfers described in both IRC
    Section368(a)(2)(C) and Treas. Reg. Section1.368-2, and transfers described
    in Treas. Reg. Section1.368-1(d); or (e) cause Company to distribute to
    Parent or any of its subsidiaries any assets of Company or the proceeds of
    any borrowing incurred by Company.

        8.  Subsidiary will have no liabilities assumed by Company, and will not
    transfer to Company any assets subject to liabilities, in the Merger.

        9.  Following the Merger, Company (or Parent) will continue Company's
    historic business assets or use a significant portion of Company's historic
    business assets in a business. To the best of Parent's knowledge, no assets
    of Company have been disposed of in any manner prior to the Merger nor does
    Company have any plan or intention to dispose of any such assets, except in
    the ordinary course of business.

        10.  Parent will pay or assume no expenses of Company other than
    expenses that are solely and directly related to the Merger in accordance
    with the guidelines established in Rev. Rul. 73-54, 1973-1 C.B. 187. Except
    as provided in the preceding sentence, Parent and Subsidiary and, to the
    best of Parent's knowledge, Company and the Company stockholders will pay
    their respective expenses, if any, incurred in connection with the Merger.

        11.  There is no intercorporate indebtedness existing between Parent and
    Company or between and Company that was issued, acquired or will be settled
    at a discount as a result of the Merger. Except as provided in the first
    sentence of paragraph 10 above, Parent will not, directly or indirectly,
    assume, or take any Company stock subject to, any fixed or contingent
    liabilities or expenses of Company or any Company stockholder in connection
    with the Merger.

        12.  In the Merger, shares of Company stock representing Control of
    Company will be exchanged solely for Parent Common Stock. For purposes of
    this representation, shares of Company stock exchanged for cash or other
    property originating with Parent will be treated as outstanding Company
    stock on the date of the Merger.

                                       2
<PAGE>
        13.  At the Effective Time (as defined in the Merger Agreement), the
    option (the "Option") described under the heading "Related Agreements-Stock
    Option Agreement" of the Registration Statement will terminate by its terms,
    to the best of Parent's knowledge, Company will not have outstanding any
    warrants, options, convertible securities, or any other type of right
    pursuant to which any person could acquire stock in Company that, if
    exercised or converted, would affect Parent's acquisition or retention of
    Control of Company.

        14.  Neither Parent nor any current or former subsidiary of Parent owns
    or has owned during the past five years, directly or indirectly, any shares
    of Company stock, or the right to acquire or vote any such shares (other
    than the Option).

        15.  Neither Parent, Subsidiary nor, to the best of Parent's knowledge,
    Company is an investment company as defined in IRC Section368(a)(2)(F).

        16.  At the Effective Time, the fair market value of the assets of
    Company will exceed the sum of its liabilities, plus the amount of
    liabilities, if any, to which the assets are subject.

        17.  To the best of Parent's knowledge, Company is not under the
    jurisdiction of a court in a Title 11 or similar case within the meaning of
    IRC Section368(a)(3)(A).

        18.  The payment of cash in lieu of fractional shares of Parent Common
    Stock is solely for the purpose of avoiding the expense and inconvenience to
    Parent of issuing fractional shares and does not represent separately
    bargained-for consideration. The total cash consideration that will be paid
    in the Merger to the Company stockholders in lieu of fractional shares of
    Parent Common Stock will not exceed one percent of the total consideration
    that will be issued in the Merger to the Company stockholders in exchange
    for their shares of Company capital stock. The fractional share interests of
    each Company stockholder will be aggregated and no Company stockholder will
    receive cash in an amount greater than the value of one full share of Parent
    Common Stock.

        19.  None of the compensation received by any Company
    stockholder-employee will be separate consideration for, or allocable to,
    any of their shares of Company stock; none of the shares of Parent Common
    Stock received by any Company stockholder-employees will be separate
    consideration for, or allocable to, any employment agreement or any
    covenants not to compete; and the compensation paid to any Company
    stockholder-employees will be for services actually rendered and will be
    commensurate with amounts paid to third parties bargaining at arm's length
    for similar services. No part of the Company stock exchanged for the Parent
    Common Stock in the Merger will be received by a Company stockholder as a
    creditor, employee or in any capacity other than that of a Company
    stockholder.

        20.  Dissenters' rights will not be exercised.

        21.  Subsidiary has been formed solely to consummate the Merger and,
    prior to the Effective Time, Subsidiary has not conducted and will not
    conduct any business activity or other operation of any kind (except for the
    issuance of its stock to Parent). Each share of Parent Common Stock is
    entitled to vote on all matters that are subject to a vote of stockholders
    under Delaware law.

        22.  No shares of Subsidiary have been or will be used as consideration
    or issued to Company stockholders in connection with the Merger.

        23.  Neither Parent nor Subsidiary will take any position on any
    federal, state or local income or franchise tax return, or take any other
    tax reporting position, that is inconsistent with the treatment of the
    Merger as a "reorganization" within the meaning of IRC Section368(a), unless
    otherwise required by a "determination" (as defined in IRC
    Section1313(a)(1)) or by applicable state or local tax law (and then only to
    the extent required by such applicable state or local tax law).

                                       3
<PAGE>
        24.  The facts relating to the contemplated merger of Subsidiary with
    and into Company as described in the filing with the Securities and Exchange
    Commission of the registration statement on Form S-4 (the "Registration
    Statement") and the representations set forth and documents described in the
    Registration Statement are, insofar as such facts pertain to Parent, true,
    correct and complete in all material respects and, to the best of Parent's
    knowledge, insofar as such facts pertain to Company, true, correct and
    complete in all material respects. The business reasons for the Merger as
    set forth in the section titled "Reasons for the Merger" of the Registration
    Statement were true and correct when stated and are true and correct as of
    the date hereof. The terms of the Merger Agreement and all other agreements
    entered into in connection therewith are the product of negotiations between
    unrelated parties negotiating at arms-length without duress or hardship.

    Parent understands the foregoing representations and has had the opportunity
to investigate and seek professional advice regarding these representations,
their meaning and factual support therefor.

    Parent recognizes that (i) your opinion relating to the federal income tax
consequences of the Merger will be based on the representations set forth herein
and on the statements contained in the Merger Agreement and the documents
related thereto, (ii) your opinion will be subject to certain limitations and
qualifications including that the opinion may not be relied upon if any such
representations are not accurate in all material respects, (iii) your opinion
will be used as the basis for Company's reporting of the Merger for federal
income tax and other purposes, and (iv) your opinion will not address any tax
consequences of the Merger or any action taken in connection therewith except as
expressly set forth in such opinions.

    The undersigned has authority to sign this representation letter on behalf
of Parent and is an executive officer of Parent fully familiar with its
operations and ownership.

<TABLE>
<S>                                                    <C>  <C>
                                                       Very truly yours,

                                                       DOUBLECLICK, INC.

                                                       By:  /s/ ELIZABETH WANG
                                                            -----------------------------------------
                                                            Name: Elizabeth Wang
                                                            Title:  Assistant Secretary
</TABLE>

                                       4
<PAGE>
                                                                       EXHIBIT B

                             [ABACUS DIRECT LETTERHEAD]

Parker Chapin Flattau & Klimpl, LLP
1211 Avenue of the Americas                                     October 20, 1999
New York, New York 10036

        Re: TAX REPRESENTATIONS FOR REVERSE TRIANGULAR MERGER

Dear Sir:

    This letter is being furnished in connection with the merger (the "Merger")
of Atlanta Merger Corp. ("Subsidiary"), a Delaware corporation and a
wholly-owned subsidiary of DoubleClick, Inc. ("Parent"), a Delaware corporation,
with and into Abacus Direct Corporation ("Company"), a Delaware corporation, in
exchange for shares of voting common stock, $0.001 par value per share, of
Parent ("Parent Common Stock") pursuant to the Agreement and Plan of Merger (the
"Merger Agreement") dated as of June 13, 1999 among Parent, Subsidiary, and
Company.(1)

    In connection with the above, Company represents and warrants as follows:

        1.  The fair market value of the Parent Common Stock and other
    consideration received by each Company stockholder in the Merger is
    approximately equal to the fair market value of the Company stock
    surrendered by each Company stockholder in the Merger.

        2.  At least 50 percent of the aggregate value of all Company stock
    outstanding immediately prior to the Merger is preserved in the Merger
    within the meaning of Treas. Reg. Section1.368-1(e). For purposes of this
    representation, the value of a share of Company stock is considered to be
    preserved in the Merger if the share of Company stock is exchanged for
    Parent Common Stock in the Merger. However, the value of a share of Company
    stock is not preserved in the Merger (and is treated as outstanding
    immediately prior to the Merger) if and to the extent that (a) in connection
    with the Merger, the share of Company stock is acquired by Parent or a
    person related to Parent for consideration other than the Parent Common
    Stock, (b) if, prior to the Merger, the share of Company stock was redeemed
    by Company or acquired by a person related to Company, (c) if, in connection
    with the Merger, the Parent Common Stock issued in the Merger is redeemed or
    acquired by a person related to Parent, or (d) to the extent that prior to
    and in connection with the Merger, an extraordinary distribution (as such
    term is used in Treas. Reg. Section1.368-1T(e)) is made with respect to the
    share of Company stock. For purposes of this representation, persons are
    considered related if they are related within the meaning of Treas. Reg.
    Section1.368-1(e)(3).

        3.  Following the Merger, Company will hold (a) at least 90% of the fair
    market value of its net assets and at least 70% of the fair market value of
    its gross assets held immediately prior to the Merger, and (b) at least 90%
    of the fair market value of Subsidiary's net assets and at least 70% of the
    fair market value of Subsidiary's gross assets held immediately prior to the
    Merger. For purposes of the preceding sentence, amounts paid to the Company
    stockholders who receive cash or other property (including cash for
    fractional shares), amounts used by Company or Subsidiary to pay
    reorganization expenses, all redemptions and distributions (except for
    regular, normal dividends) made by Company and all assets disposed of by
    Company in contemplation of the Merger (except in the ordinary course of
    business) will be included in the assets of Company or Subsidiary, as the
    case may be, immediately prior to the Merger.

        4.  To the best of Company's knowledge, prior to the Merger, Parent will
    be in Control of Subsidiary. As used herein, "Control" of a corporation
    means control as defined by IRC Section368(c) which defines control
    generally to mean ownership of stock possessing at least 80% of the total
    combined voting power of all classes of stock entitled to vote and at least
    eighty 80% of the total

- ------------------------
(1)  Unless otherwise noted herein, all section references are to the Internal
Revenue Code of 1986 ("IRC") and to the regulations ("Treas. Reg.") promulgated
thereunder, as either may be amended or otherwise modified.
<PAGE>
    number of shares of all other classes of stock of the corporation. For
    purposes of determining Control, a person will not be considered to own
    voting stock if rights to vote such stock (or to restrict or otherwise
    control the voting of such stock) are held by a third party (including a
    voting trust) other than an agent of such person.

        5.  Company has no present plan or intention to issue additional shares
    of its stock that would result in Parent's losing Control of Company.

        6.  To the best of Company's knowledge, Parent has no present plan or
    intention to reacquire, or to cause any corporation related to Parent to
    acquire, any Parent Common Stock following the Merger, and no corporation
    related to Parent has a present plan or intention to purchase any Parent
    Common Stock. For purposes of the preceding sentence, persons are considered
    related if such persons are related within the meaning of Treas. Reg.
    Section1.368-1(e)(3). Neither Company nor any person related to Company has
    redeemed or acquired, nor does Company or any person related to Company have
    any plan or intention to redeem or acquire, any shares of Company stock or
    make an extraordinary distribution with respect to any shares of Company
    stock. For purposes of the preceding sentence, persons are considered
    related if such persons are related within the meaning of Treas. Reg.
    Section1.368-1T(e)(2)(ii).

        7.  Except as described in the Registration Statement (as defined in
    paragraph 24 below) and to the best of Company's knowledge, Parent has no
    present plan or intention to otherwise (a) liquidate Company; (b) merge
    Company with or into another corporation; (c) sell, distribute or otherwise
    dispose of Company capital stock; (d) cause Company to sell or otherwise
    dispose of any of its assets (or any assets acquired from Subsidiary),
    except for dispositions made in the ordinary course of business, transfers
    described in both IRC Section368(a)(2)(C) and Treas. Reg. Section1.368-2,
    and transfers described in Treas. Reg. Section1.368-1(d); or (e) cause
    Company to distribute to Parent or any of its subsidiaries any assets of
    Company or the proceeds of any borrowing incurred by Company.

        8.  To the best of Company's knowledge, Subsidiary will have no
    liabilities assumed by Company, and will not transfer to Company any assets
    subject to liabilities, in the Merger.

        9.  To the best of Company's knowledge, following the Merger, Company
    (or Parent) will continue Company's historic business or use a significant
    portion of Company's historic business assets in a business. No assets of
    Company have been disposed of in any manner prior to the Merger nor does
    Company have any plan or intention to dispose of any such assets, except in
    the ordinary course of business.

        10. Parent will pay or assume only those expenses of Company that are
    solely and directly related to the Merger in accordance with the guidelines
    established in Rev. Rul. 73-54, 1973-1 C.B. 187. Except as provided in the
    preceding sentence, Parent, Subsidiary, Company, and the Company
    stockholders will pay their respective expenses, if any, incurred in
    connection with the Merger.

        11. There is no intercorporate indebtedness existing between Parent and
    Company or between and Company that was issued, acquired or will be settled
    at a discount as a result of the Merger. Except as provided in the first
    sentence of paragraph 10 above, Parent will not, directly or indirectly,
    assume, or take any Company stock subject to, any fixed or contingent
    liabilities or expenses of Company or any Company stockholder in connection
    with the Merger.

        12. In the Merger, shares of Company stock representing Control of
    Company will be exchanged solely for Parent Common Stock. For purposes of
    this representation, shares of Company stock exchanged for cash or other
    property originating with Parent will be treated as outstanding Company
    stock on the date of the Merger.

        13. At the Effective Time (as defined in the Merger Agreement), the
    option (the "Option") described under the heading "Related Agreements-Stock
    Option Agreement" of the Registration

                                       2
<PAGE>
    Statement will terminate by its terms, and Company will not have outstanding
    any warrants, options, convertible securities, or any other type of right
    pursuant to which any person could acquire stock in Company that, if
    exercised or converted, would affect Parent's acquisition or retention of
    Control of Company.

        14. Neither Parent nor any current or former subsidiary of Parent owns
    or has owned during the past five years, as of record, any shares of Company
    stock, or the right to acquire or vote any such shares (other than the
    Option). To the best of Company's knowledge, neither Parent nor any current
    or former subsidiary of Parent owns or has owned, indirectly or otherwise
    (other than as a stockholder of record), during the past five years any
    shares of Company stock, or the right to acquire or vote any such shares
    (other than the Option).

        15. Neither Company nor, to the best of Company's knowledge, Parent or
    Subsidiary is an investment company as defined in IRC Section368(a)(2)(F).

        16. At the Effective Time, the fair market value of the assets of
    Company will exceed the sum of its liabilities, plus the amount of
    liabilities, if any, to which the assets are subject.

        17. Company is not under the jurisdiction of a court in a Title 11 or
    similar case within the meaning of IRC Section368(a)(3)(A).

        18. The payment of cash in lieu of fractional shares of Parent Common
    Stock is solely for the purpose of avoiding the expense and inconvenience to
    Parent of issuing fractional shares and does not represent separately
    bargained-for consideration. The total cash consideration that will be paid
    in the Merger to the Company stockholders in lieu of fractional shares of
    Parent Common Stock will not exceed one percent of the total consideration
    that will be issued in the Merger to the Company stockholders in exchange
    for their shares of Company capital stock. The fractional share interests of
    each Company stockholder will be aggregated and no Company stockholder will
    receive cash in an amount greater than the value of one full share of Parent
    Common Stock.

        19. None of the compensation received by any Company
    stockholder-employee will be separate consideration for, or allocable to,
    any of their shares of Company stock; none of the shares of Parent Common
    Stock received by any Company stockholder-employees will be separate
    consideration for, or allocable to, any employment agreement or any
    covenants not to compete; and the compensation paid to any Company
    stockholder-employees will be for services actually rendered and will be
    commensurate with amounts paid to third parties bargaining at arm's length
    for similar services. No part of the Company stock exchanged for the Parent
    Common Stock in the Merger will be received by a Company stockholder as a
    creditor, employee or in any capacity other than that of a Company
    stockholder.

        20. Dissenters' rights will not be exercised.

        21. To the best of Company's knowledge, Subsidiary has been formed
    solely to consummate the Merger and, prior to the Effective Time, Subsidiary
    has not conducted and will not conduct any business activity or other
    operation of any kind (except for the issuance of its stock to Parent). Each
    share of Parent Common Stock is entitled to vote on all matters that are
    subject to a vote of stockholders under Delaware law.

        22. No shares of Subsidiary have been or will be used as consideration
    or issued to Company stockholders in connection with the Merger.

        23. Neither Parent nor Subsidiary will take any position on any federal,
    state or local income or franchise tax return, or take any other tax
    reporting position, that is inconsistent with the treatment of the Merger as
    a "reorganization" within the meaning of IRC Section368(a), unless otherwise
    required by a "determination" (as defined in IRC Section1313(a)(1)) or by
    applicable state or local tax law (and then only to the extent required by
    such applicable state or local tax law).

                                       3
<PAGE>
        24. The facts relating to the contemplated merger of Subsidiary with and
    into Company as described in the filing with the Securities and Exchange
    Commission of the registration statement on Form S-4 (the "Registration
    Statement") and the representations set forth and documents described in the
    Registration Statement are, insofar as such facts pertain to Company, true,
    correct and complete in all material respects and, to the best of Company's
    knowledge, insofar as such facts pertain to Parent, true, correct and
    complete in all material respects. The business reasons for the Merger as
    set forth in the section titled "Reasons for the Merger" of the Registration
    Statement were true and correct when stated and are true and correct as of
    the date hereof. The terms of the Merger Agreement and all other agreements
    entered into in connection therewith are the product of negotiations between
    unrelated parties negotiating at arms-length without duress or hardship.

    Company understands the foregoing representations and has had the
opportunity to investigate and seek professional advice regarding these
representations, their meaning and factual support therefor.

    Company recognizes that (i) your opinion relating to the federal income tax
consequences of the Merger will be based on the representations set forth herein
and on the statements contained in the Merger Agreement and the documents
related thereto, (ii) your opinion will be subject to certain limitations and
qualifications including that the opinion may not be relied upon if any such
representations are not accurate in all material respects, (iii) your opinion
will be used as the basis for Company's reporting of the Merger for federal
income tax and other purposes, and (iv) your opinion will not address any tax
consequences of the Merger or any action taken in connection therewith except as
expressly set forth in such opinions.

    The undersigned has authority to sign this representation letter on behalf
of Company and is an executive officer of Company fully familiar with its
operations and ownership.

                                          Very truly yours,

                                          Abacus Direct Corporation

                                          By: /s/ CARLOS E. SALA
   -----------------------------------------------------------------------------

                                          NAME: CARLOS E. SALA
                                            TITLE: SENIOR VICE
                                          PRESIDENT--FINANCE

                                       4

<PAGE>

                                                                    Exhibit 10.1

                                DOUBLECLICK INC.
                        1999 EMPLOYEE STOCK PURCHASE PLAN

         I.       PURPOSE OF THE PLAN

                  This Employee Stock Purchase Plan is intended to promote the
interests of DoubleClick Inc., a Delaware corporation, by providing eligible
employees with the opportunity to acquire a proprietary interest in the
Corporation through participation in a payroll-deduction based employee stock
purchase plan designed to qualify under Section 423 of the Code.

                  Capitalized terms herein shall have the meanings assigned to
such terms in the attached Appendix.

         II.      ADMINISTRATION OF THE PLAN

                  The Plan Administrator shall have full authority to interpret
and construe any provision of the Plan and to adopt such rules and regulations
for administering the Plan as it may deem necessary in order to comply with the
requirements of Code Section 423. Decisions of the Plan Administrator shall be
final and binding on all parties having an interest in the Plan.

         III.     STOCK SUBJECT TO PLAN

                  A. The stock purchasable under the Plan shall be shares of
authorized but unissued or reacquired Common Stock, including shares of Common
Stock purchased on the open market. The number of shares of Common Stock
initially reserved for issuance over the term of the Plan shall initially be
limited to 500,000 shares.

                  B. The number of shares of Common Stock available for issuance
under the Plan shall automatically increase on the first trading day of January
each calendar year during the term of the Plan, beginning with calendar year
2001, by an amount equal to one percent (1%) of the total number of shares of
Common Stock outstanding on the last trading day in December of the immediately
preceding calendar year, but in no event shall any such annual increase exceed
450,000 shares.

                  C. Should any change be made to the Common Stock by reason of
any stock split, stock dividend, recapitalization, combination of shares,
exchange of shares or other change affecting the outstanding Common Stock as a
class without the Corporation's receipt of consideration, appropriate
adjustments shall be made to (i) the maximum number and class of securities
issuable under the Plan, (ii) the maximum number and class of securities
purchasable per Participant on any one Purchase Date, (iii) the maximum number
and class of securities purchasable by all Participants in the aggregate on any
one Purchase Date, (iv) the maximum number and/or class of securities by which
the share reserve is to increase automatically each calendar year pursuant to
the provisions of Section III.B of this Article One and (v) the number and class
of securities and the price per share in effect under each outstanding purchase
right in order to prevent the dilution or enlargement of benefits thereunder.
<PAGE>

         IV.      OFFERING PERIODS

                  A. Shares of Common Stock shall be offered for purchase under
the Plan through a series of successive offering periods until such time as (i)
the maximum number of shares of Common Stock available for issuance under the
Plan shall have been purchased or (ii) the Plan shall have been sooner
terminated.

                  B. Each offering period shall be of such duration not to
exceed twenty-four (24) months as determined by the Plan Administrator prior to
the start date of such offering period. The initial offering period shall
commence on the Effective Date and terminate as designated by the Plan
Administrator.

                  C. Each offering period shall be comprised of a series of one
or more successive Purchase Periods. The length of each Purchase Period during
an offering period shall be determined by the Plan Administrator prior to the
commencement of that offering period. The first Purchase Period shall commence
on the Effective Date.

                  D. Should the Fair Market Value per share of Common Stock on
any Purchase Date within an offering period be less than the Fair Market Value
per share of Common Stock on the start date of that offering period, then that
offering period shall automatically terminate immediately after the purchase of
shares of Common Stock on such Purchase Date, and a new offering period shall
commence on the next business day following such Purchase Date. The duration of
the new offering period shall be established by the Plan Administrator (not to
exceed twenty (24) months) within five (5) business days following the start
date of that offering period.

         V.       ELIGIBILITY

                  A. Each individual who is an Eligible Employee on the start
date of any offering period under the Plan may enter that offering period on
such start date or on any subsequent Entry Date within that offering period,
provided he or she remains an Eligible Employee.

                  B. Each individual who first becomes an Eligible Employee
after the start date of an offering period may enter that offering period on any
subsequent Entry Date within that offering period on which he or she is an
Eligible Employee.

                  C. The date an individual enters an offering period shall be
designated his or her Entry Date for purposes of that offering period.

                  D. To participate in the Plan for a particular offering
period, the Eligible Employee must complete the enrollment forms prescribed by
the Plan Administrator (including a stock purchase agreement and a payroll
deduction authorization) and file such forms with the Plan Administrator (or its
designate) on or before his or her scheduled Entry Date.


                                       2
<PAGE>

         VI.      PAYROLL DEDUCTIONS

                  A. The payroll deduction authorized by the Participant for
purposes of acquiring shares of Common Stock during an offering period may be
any multiple of one percent (1%) of the Cash Compensation paid to the
Participant during each Purchase Period within that offering period. The maximum
amount of payroll deduction authorized for purchases during any calendar year
under the Purchase Plan and any other employee stock purchase plan maintained by
the Corporation or any Corporate Affiliate (including the NetGravity, Inc. 1998
Employee Stock Purchase Plan assumed by the Corporation) may not to exceed ten
percent (10%) of the Participant's Cash Compensation for each year. The Plan
Administrator shall have the discretionary authority, exercisable prior to the
start of any offering period to provide that the payroll deductions shall be
based on the Base Salary paid to the Participant and to designate the maximum
payroll deduction in effect (not to exceed ten percent (10%)) for that offering
period.

                  B. The deduction rate authorized by the Participant shall
continue in effect throughout the offering period, except to the extent such
rate is changed in accordance with the following guidelines:

                           (i) The Participant may, at any time during the
                  offering period, reduce his or her rate of payroll deduction
                  to become effective as soon as possible after filing the
                  appropriate form with the Plan Administrator. The Participant
                  may not, however, effect more than one (1) such reduction per
                  Purchase Period.

                           (ii) The Participant may, prior to the commencement
                  of any new Purchase Period within the offering period,
                  increase the rate of his or her payroll deduction by filing
                  the appropriate form with the Plan Administrator. The new rate
                  (which may not exceed the ten percent (10%) maximum (or such
                  other maximum designated by the Plan Administrator) shall
                  become effective on the start date of the first Purchase
                  Period following the filing of such form.

                  B. Payroll deductions shall begin on the first pay day
administratively feasible following the Participant's Entry Date into the
offering period and shall (unless sooner terminated by the Participant) continue
through the pay day ending with or immediately prior to the last day of that
offering period. The amounts so collected shall be credited to the Participant's
book account under the Plan, but no interest shall be paid on the balance from
time to time outstanding in such account. The amounts collected from the
Participant shall not be required to be held in any segregated account or trust
fund and may be commingled with the general assets of the Corporation and used
for general corporate purposes.

                  C. Payroll deductions shall automatically cease upon the
termination of the Participant's purchase right in accordance with the
provisions of the Plan.

                  D. The Participant's acquisition of Common Stock under the
Plan on any Purchase Date shall neither limit nor require the Participant's
acquisition of Common Stock on any subsequent Purchase Date, whether within the
same or a different offering period.


                                       3
<PAGE>

         VII.     PURCHASE RIGHTS

                  A. GRANT OF PURCHASE RIGHT. A Participant shall be granted a
separate purchase right for each offering period in which he or she
participates. The purchase right shall be granted on the Participant's Entry
Date into the offering period and shall provide the Participant with the right
to purchase shares of Common Stock, in a series of successive installments over
the remainder of such offering period, upon the terms set forth below. The
Participant shall execute a stock purchase agreement embodying such terms and
such other provisions (not inconsistent with the Plan) as the Plan Administrator
may deem advisable.

                  Under no circumstances shall purchase rights be granted under
the Plan to any Eligible Employee if such individual would, immediately after
the grant, own (within the meaning of Code Section 424(d)) or hold outstanding
options or other rights to purchase, stock possessing five percent (5%) or more
of the total combined voting power or value of all classes of stock of the
Corporation or any Corporate Affiliate.

                  B. EXERCISE OF THE PURCHASE RIGHT. Each purchase right shall
be automatically exercised in installments on each successive Purchase Date
within the offering period, and shares of Common Stock shall accordingly be
purchased on behalf of each Participant on each such Purchase Date. The purchase
shall be effected by applying the Participant's payroll deductions for the
Purchase Period ending on such Purchase Date to the purchase of whole shares of
Common Stock at the purchase price in effect for the Participant for that
Purchase Date.

                  C. PURCHASE PRICE. The purchase price per share at which
Common Stock will be purchased on the Participant's behalf on each Purchase Date
within the offering period shall be equal to eighty-five percent (85%) of the
lower of (i) the Fair Market Value per share of Common Stock on the
Participant's Entry Date into that offering period or (ii) the Fair Market Value
per share of Common Stock on that Purchase Date.

                  D. NUMBER OF PURCHASABLE SHARES. The number of shares of
Common Stock purchasable by a Participant on each Purchase Date during the
offering period shall be the number of whole shares obtained by dividing the
amount collected from the Participant through payroll deductions during the
Purchase Period ending with that Purchase Date by the purchase price in effect
for the Participant for that Purchase Date. However, the maximum number of
shares of Common Stock purchasable per Participant on any one Purchase Date
shall not exceed 250 shares, subject to periodic adjustments in the event of
certain changes in the Corporation's capitalization. In addition, the maximum
aggregate number of shares of Common Stock purchasable by all Participants on
any one Purchase Date shall not exceed 125,000 shares, subject to periodic
adjustments in the event of certain changes in the Corporation's capitalization.
The Plan Administrator shall have the discretionary authority, exercisable prior
to the start of any offering period under the Plan, to increase or decrease the
limitations to be in effect for the number of shares purchasable per Participant
and in the aggregate by all Participants on each Purchase Date during that
offering period.


                                       4
<PAGE>

                  E. EXCESS PAYROLL DEDUCTIONS. Any payroll deductions not
applied to the purchase of shares of Common Stock on any Purchase Date because
they are not sufficient to purchase a whole share of Common Stock shall be held
for the purchase of Common Stock on the next Purchase Date. However, any payroll
deductions not applied to the purchase of Common Stock by reason of the
limitation on the maximum number of shares purchasable per Participant or in the
aggregate on the Purchase Date shall be promptly refunded.

                  F. TERMINATION OF PURCHASE RIGHT. The following provisions
shall govern the termination of outstanding purchase rights:

                           (i) A Participant may, at any time prior to the next
                  scheduled Purchase Date in the offering period, terminate his
                  or her outstanding purchase right by filing the appropriate
                  form with the Plan Administrator (or its designate), and no
                  further payroll deductions shall be collected from the
                  Participant with respect to the terminated purchase right. Any
                  payroll deductions collected during the Purchase Period in
                  which such termination occurs shall, at the Participant's
                  election, be immediately refunded or held for the purchase of
                  shares on the next Purchase Date. If no such election is made
                  at the time such purchase right is terminated, then the
                  payroll deductions collected with respect to the terminated
                  right shall be refunded as soon as possible.

                           (ii) The termination of such purchase right shall be
                  irrevocable, and the Participant may not subsequently rejoin
                  the Purchase Period for which the terminated purchase right
                  was granted. In order to resume participation in any
                  subsequent Purchase Period, such individual must re-enroll in
                  the Plan (by making timely filing of the prescribed enrollment
                  forms) on or before the start date of the new Purchase Period.

                           (iii) Should the Participant cease to remain an
                  Eligible Employee for any reason (including death, disability
                  or change in status) while his or her purchase right remains
                  outstanding, then that purchase right shall immediately
                  terminate, and all of the Participant's payroll deductions for
                  the Purchase Period in which the purchase right so terminates
                  shall be immediately refunded. However, should the Participant
                  cease to remain in active service by reason of an approved
                  unpaid leave of absence, then the Participant shall have the
                  right, exercisable up until the last business day of the
                  Purchase Period in which such leave commences, to (a) withdraw
                  all the payroll deductions collected to date on his or her
                  behalf for that Purchase Period or (b) have such funds held
                  for the purchase of shares on his or her behalf on the next
                  scheduled Purchase Date. In no event, however, shall any
                  further payroll deductions be collected on the Participant's
                  behalf during such leave. Upon the Participant's return to
                  active service (x) within ninety (90) days following the
                  commencement of such leave or (y) prior to the expiration of
                  any longer period for which such Participant's right to
                  reemployment with the Corporation is guaranteed by statute or
                  contract, his or her payroll deductions under the Plan shall
                  automatically resume at the rate in effect at the time the
                  leave began, unless the Participant withdraws from the Plan
                  prior to his or her return. An individual who returns to
                  active employment


                                       5
<PAGE>

                  following a leave of absence which exceeds in duration the
                  applicable (x) or (y) time period shall be treated as a new
                  Employee for purposes of subsequent participation in the Plan
                  and must accordingly re-enroll in the Plan (by making a timely
                  filing of the prescribed enrollment forms) on or before his or
                  her scheduled Entry Date into the offering period.

                  G. CHANGE IN CONTROL. Each outstanding purchase right shall
automatically be exercised, immediately prior to the effective date of any
Change in Control, by applying the payroll deductions of each Participant for
the Purchase Period in which such Change in Control occurs to the purchase of
whole shares of Common Stock at a purchase price per share equal to eighty-five
percent (85%) of the lower of (i) the Fair Market Value per share of Common
Stock on the Participant's Entry Date into the offering period in which such
Change in Control occurs or (ii) the Fair Market Value per share of Common Stock
immediately prior to the effective date of such Change in Control. However, the
applicable limitation on the number of shares of Common Stock purchasable per
Participant shall continue to apply to any such purchase, but not the limitation
applicable to the maximum number of shares of Common Stock purchasable in the
aggregate.

                  The Corporation shall use its best efforts to provide at least
ten (10)-days prior written notice of the occurrence of any Change in Control,
and Participants shall, following the receipt of such notice, have the right to
terminate their outstanding purchase rights prior to the effective date of the
Change in Control.

                  H. PRORATION OF PURCHASE RIGHTS. Should the total number of
shares of Common Stock to be purchased pursuant to outstanding purchase rights
on any particular date exceed the number of shares then available for issuance
under the Plan, the Plan Administrator shall make a pro-rata allocation of the
available shares on a uniform and nondiscriminatory basis, and the payroll
deductions of each Participant, to the extent in excess of the aggregate
purchase price payable for the Common Stock pro-rated to such individual, shall
be refunded.

                  I. ASSIGNABILITY. The purchase right shall be exercisable only
by the Participant and shall not be assignable or transferable by the
Participant.

                  J. STOCKHOLDER RIGHTS. A Participant shall have no stockholder
rights with respect to the shares subject to his or her outstanding purchase
right until the shares are purchased on the Participant's behalf in accordance
with the provisions of the Plan and the Participant has become a holder of
record of the purchased shares.

         VIII.    ACCRUAL LIMITATIONS

                  A. No Participant shall be entitled to accrue rights to
acquire Common Stock pursuant to any purchase right outstanding under this Plan
if and to the extent such accrual, when aggregated with (i) rights to purchase
Common Stock accrued under any other purchase right granted under this Plan and
(ii) similar rights accrued under other employee stock purchase plans (within
the meaning of Code Section 423) of the Corporation or any Corporate Affiliate,
would otherwise permit such Participant to purchase more than Twenty-Five
Thousand Dollars ($25,000.00) worth of stock of the Corporation or any Corporate
Affiliate (determined on the


                                       6
<PAGE>

basis of the Fair Market Value per share on the date or dates such rights are
granted) for each calendar year such rights are at any time outstanding.

                  B. For purposes of applying such accrual limitations to the
purchase rights granted under the Plan, the following provisions shall be in
effect:

                           (i) The right to acquire Common Stock under each
                  outstanding purchase right shall accrue in a series of
                  installments on each successive Purchase Date during the
                  offering period on which such right remains outstanding.

                           (ii) No right to acquire Common Stock under any
                  outstanding purchase right shall accrue to the extent the
                  Participant has already accrued in the same calendar year the
                  right to acquire Common Stock under one or more other purchase
                  rights at a rate equal to Twenty-Five Thousand Dollars
                  ($25,000.00) worth of Common Stock (determined on the basis of
                  the Fair Market Value per share on the date or dates of grant)
                  for each calendar year such rights were at any time
                  outstanding.

                  C. If by reason of such accrual limitations, any purchase
right of a Participant does not accrue for a particular Purchase Period, then
the payroll deductions which the Participant made during that Purchase Period
with respect to such purchase right shall be promptly refunded.

                  D. In the event there is any conflict between the provisions
of this Article and one or more provisions of the Plan or any instrument issued
thereunder, the provisions of this Article shall be controlling.

         IX.      EFFECTIVE DATE AND TERM OF THE PLAN

                  A. The Plan was adopted by the Board on October ___, 1999 and
shall become effective at the Effective Time, provided no purchase rights
granted under the Plan shall be exercised, and no shares of Common Stock shall
be issued hereunder, until (i) the Plan shall have been approved by the
stockholders of the Corporation and (ii) the Corporation shall have complied
with all applicable requirements of the 1933 Act (including the registration of
the shares of Common Stock issuable under the Plan on a Form S-8 registration
statement filed with the Securities and Exchange Commission), all applicable
listing requirements of any stock exchange (or the Nasdaq National Market, if
applicable) on which the Common Stock is listed for trading and all other
applicable requirements established by law or regulation. In the event such
stockholder approval is not obtained, or such compliance is not effected, within
twelve (12) months after the date on which the Plan is adopted by the Board, the
Plan shall terminate and have no further force or effect.

                  B. Unless sooner terminated by the Board, the Plan shall
terminate upon the earliest of (i) the last business day in January 2010, (ii)
the date on which all shares available for issuance under the Plan shall have
been sold pursuant to purchase rights exercised under the Plan or (iii) the date
on which all purchase rights are exercised in connection with a Corporate


                                       7
<PAGE>

Transaction. No further purchase rights shall be granted or exercised, and no
further payroll deductions shall be collected, under the Plan following such
termination.

         X.       AMENDMENT OF THE PLAN

                  A. The Board may alter, amend, suspend or terminate the Plan
at any time to become effective immediately following the close of any Purchase
Period. However, the Plan may be amended or terminated immediately upon Board
action, if and to the extent necessary to assure that the Corporation will not
recognize, for financial reporting purposes, any compensation expense in
connection with the shares of Common Stock offered for purchase under the Plan,
should the financial accounting rules applicable to the Plan at the Effective
Time be subsequently revised so as to require the recognition of compensation
expense in the absence of such amendment or termination.

                  B. In no event may the Board effect any of the following
amendments or revisions to the Plan without the approval of the Corporation's
stockholders: (i) increase the number of shares of Common Stock issuable under
the Plan, except for permissible adjustments in the event of certain changes in
the Corporation's capitalization, (ii) alter the purchase price formula so as to
reduce the purchase price payable for the shares of Common Stock purchasable
under the Plan or (iii) modify the eligibility requirements for participation in
the Plan.

         XI.      GENERAL PROVISIONS

                  A. All costs and expenses incurred in the administration of
the Plan shall be paid by the Corporation; however, each Plan Participant shall
bear all costs and expenses incurred by such individual in the sale or other
disposition of any shares purchased under the Plan.

                  B. Nothing in the Plan shall confer upon the Participant any
right to continue in the employ of the Corporation or any Corporate Affiliate
for any period of specific duration or interfere with or otherwise restrict in
any way the rights of the Corporation (or any Corporate Affiliate employing such
person) or of the Participant, which rights are hereby expressly reserved by
each, to terminate such person's employment at any time for any reason, with or
without cause.

                  C. The provisions of the Plan shall be governed by the laws of
the State of New York without resort to that State's conflict-of-laws rules.


                                       8
<PAGE>

                                   SCHEDULE A
                                   ----------

                          CORPORATIONS PARTICIPATING IN
                        1999 EMPLOYEE STOCK PURCHASE PLAN
                            AS OF THE EFFECTIVE DATE
                            ------------------------

                                DoubleClick Inc.
<PAGE>

                                    APPENDIX

                  The following definitions shall be in effect under the Plan:

                  A. BOARD shall mean the Corporation's Board of Directors.

                  B. BASE SALARY shall mean the regular base salary paid to a
Participant by one or more Participating Companies during such individual's
period of participating in the Plan, plus any pre-tax contributions made by the
Participant to any Code Section 401(k) salary deferral plan or any Code Section
125 cafeteria benefit program now or hereafter established by the Corporation or
any Corporate Affiliate.

                  C. CASH EARNINGS shall mean the (i) regular base salary paid
to a Participant by one or more Participating Companies during such individual's
period of participation in one or more offering periods under the Plan plus (ii)
all overtime payments, bonuses, commissions, profit-sharing distributions and
other incentive-type payments received during such period. Such Cash Earnings
shall be calculated before deduction of (A) any income or employment tax
withholdings or (B) any and all contributions made by the Participant to any
Code Section 401(k) salary deferral plan or Code Section 125 cafeteria benefit
program now or hereafter established by the Corporation or any Corporate
Affiliate. However, Cash Earnings shall NOT include any contributions made on
the Participant's behalf by the Corporation or any Corporate Affiliate to any
employee benefit or welfare plan now or hereafter established (other than Code
Section 401(k) or Code Section 125 contributions deducted from such Cash
Earnings).

                  D. CHANGE IN CONTROL shall mean a change in ownership of the
Corporation pursuant to any of the following transactions:

                        (i) a merger or consolidation in which securities
         possessing more than fifty percent (50%) of the total combined voting
         power of the Corporation's outstanding securities are transferred to a
         person or persons different from the persons holding those securities
         immediately prior to such transaction, or

                        (ii) the sale, transfer or other disposition of all or
         substantially all of the assets of the Corporation in complete
         liquidation or dissolution of the Corporation, or

                        (iii) the acquisition, directly or indirectly by an
         person or related group of persons (other than the Corporation or a
         person that directly or indirectly controls, is controlled by or is
         under common control with the Corporation) of beneficial ownership
         (within the meaning of Rule 13d-3 of the 1934 Act) of securities
         possessing more than fifty percent (50%) of the total combined voting
         power of the Corporation's outstanding securities pursuant to a tender
         or exchange offer made directly to the Corporation's stockholders.

                  E. CODE shall mean the Internal Revenue Code of 1986, as
amended.


                                      A-1
<PAGE>

                  F. COMMON STOCK shall mean the Corporation's common stock.

                  G. CORPORATE AFFILIATE shall mean any parent or subsidiary
corporation of the Corporation (as determined in accordance with Code Section
424), whether now existing or subsequently established.

                  H. CORPORATION shall mean DoubleClick Inc., a Delaware
corporation, and any corporate successor to all or substantially all of the
assets or voting stock of DoubleClick Inc., which shall by appropriate action
adopt the Plan.

                  I. EFFECTIVE DATE shall mean February 1, 2000. Any Corporate
Affiliate which becomes a Participating Corporation after such Effective Date
shall designate a subsequent Effective Date with respect to its
employee-Participants.

                  J. ELIGIBLE EMPLOYEE shall mean any person who is employed by
a Participating Corporation on a basis under which he or she is regularly
expected to render more than twenty (20) hours of service per week for more than
five (5) months per calendar year for earnings considered wages under Code
Section 3401(a).

                  K. ENTRY DATE shall mean the date an Eligible Employee first
commences participation in the offering period in effect under the Plan. The
earliest Entry Date under the Plan shall be the Effective Date.

                  L. FAIR MARKET VALUE per share of Common Stock on any relevant
date shall be determined in accordance with the following provisions:

                        (i) If the Common Stock is at the time traded on the
         Nasdaq National Market, then the Fair Market Value shall be the closing
         selling price per share of Common Stock on the date in question, as
         such price is reported by the National Association of Securities
         Dealers on the Nasdaq National Market. If there is no closing selling
         price for the Common Stock on the date in question, then the Fair
         Market Value shall be the closing selling price on the last preceding
         date for which such quotation exists.

                       (ii) If the Common Stock is at the time listed on any
         Stock Exchange, then the Fair Market Value shall be the closing selling
         price per share of Common Stock on the date in question on the Stock
         Exchange determined by the Plan Administrator to be the primary market
         for the Common Stock, as such price is officially quoted in the
         composite tape of transactions on such exchange. If there is no closing
         selling price for the Common Stock on the date in question, then the
         Fair Market Value shall be the closing selling price on the last
         preceding date for which such quotation exists.

                  M. 1933 ACT shall mean the Securities Act of 1933, as amended.

                  N. PARTICIPANT shall mean any Eligible Employee of a
Participating Corporation who is actively participating in the Plan.


                                      A-2
<PAGE>

                  O. PARTICIPATING CORPORATION shall mean the Corporation and
such Corporate Affiliate or Affiliates as may be authorized from time to time by
the Board to extend the benefits of the Plan to their Eligible Employees. The
Participating Corporations in the Plan are listed in attached Schedule A.

                  P. PLAN shall mean the Corporation's 1999 Employee Stock
Purchase Plan, as set forth in this document.

                  Q. PLAN ADMINISTRATOR shall mean the committee of two (2) or
more Board members appointed by the Board to administer the Plan.

                  R. PURCHASE DATE shall mean the last business day of each
Purchase Period.

                  S. PURCHASE PERIOD shall mean each successive period within
the offering period at the end of which there shall be purchased shares of
Common Stock on behalf of each Participant.

                  T. STOCK EXCHANGE shall mean either the American Stock
Exchange or the New York Stock Exchange.


                                      A-3

<PAGE>
                                                                    EXHIBIT 23.3

                       CONSENT OF INDEPENDENT ACCOUNTANTS

    We hereby consent to the incorporation by reference in this Registration
Statement on Form S-4 of DoubleClick Inc. of our report dated January 19, 1999
relating to the consolidated financial statements and financial statement
schedule, which appears in DoubleClick Inc.'s Annual Report on Form 10-K for the
year ended December 31, 1998. We also consent to the references to us under the
headings "Experts" and "Selected Historical Consolidated Financial Data" in such
Registration Statement.

/s/ PricewaterhouseCoopers LLP

PricewaterhouseCoopers LLP
New York, New York
October 19, 1999

<PAGE>
                                                                    Exhibit 23.4

                       CONSENT OF INDEPENDENT ACCOUNTANTS

    We hereby consent to the incorporation by reference in this Registration
Statement on Form S-4 of DoubleClick Inc. of our report dated March 1, 1999
relating to the financial statements of Abacus Direct Corporation, which appears
on page F-1 of the Abacus Direct Corporation Annual Report on Form 10-K for the
year ended December 31, 1998. We also consent to the references to us under the
headings "Abacus Direct Corporation Selected Historical Consolidated Financial
Data" and "Experts" in such Registration Statement.

/s/ PricewaterhouseCoopers LLP

PricewaterhouseCoopers LLP
Broomfield, Colorado
October 19, 1999

<PAGE>
                                                                    EXHIBIT 23.5

The Board of Directors
NetGravity, Inc.

We consent to the use of our report incorporated herein by reference and to the
reference to our firm under the heading "Experts" in this Registration
Statement.

<TABLE>
<S>                                            <C>
                                               /s/ KPMG LLP
San Francisco, California                      --------------------------------------------
October 19, 1999                               KPMG LLP
</TABLE>

<PAGE>
                                                                    EXHIBIT 23.6

PERSONAL AND CONFIDENTIAL

October 20, 1999

Board of Directors
DoubleClick Inc.
41 Madison Avenue
New York, NY 10010

Re:  Registration Statement on Form S-4 of DoubleClick Inc.

Gentlemen:

    Reference is made to our opinion letter dated June 13, 1999 with respect to
the fairness from a financial point of view to DoubleClick Inc. (the "Company")
of the exchange ratio of 1.05 shares of Common Stock, par value $0.001 per
share, of the Company to be paid for each share of Common Stock, par value
$0.001 per share, of Abacus Direct Corporation ("Abacus") pursuant to the
Agreement and Plan of Merger, dated as of June 13, 1999, between the Company,
Atlanta Merger Corp., a wholly-owned subsidiary of the Company, and Abacus.

    The foregoing opinion letter was provided for the information and assistance
of the Board of Directors of the Company in connection with its consideration of
the transaction contemplated therein and is not to be used, circulated, quoted
or otherwise referred to for any other purpose, nor is it to be filed with,
included in or referred to in whole or in part in any registration statement,
proxy statement or any other document, except in accordance with our prior
written consent. We understand that the Company has determined to include our
opinion in the above-referenced Registration Statement.

    In that regard, we hereby consent to the reference to the opinion of our
Firm under the captions "Summary of the Joint Proxy
Statement/Prospectus--Opinions of Financial Advisors", "The Merger--Background
of the Merger", "The Merger--Reasons for the Merger; Recommendations of Boards
of Directors--DoubleClick" and "The Merger--Opinions of Financial
Advisors--DoubleClick" and to the inclusion of the foregoing opinion in the
Joint Proxy Statement/Prospectus included in the above-mentioned Registration
Statement. In giving such consent, we do not thereby admit that we come within
the category of persons whose consent is required under Section 7 of the
Securities Act of 1933 or the rules and regulations of the Securities and
Exchange Commission thereunder.

                                          Very truly yours,

                                          /s/ GOLDMAN, SACHS & CO.
                                          (Goldman, Sachs & Co.)

<PAGE>
                                                                    EXHIBIT 23.7

                 CONSENT OF BANCBOSTON ROBERTSON STEPHENS INC.

    We hereby consent to the use of and reference to our opinion dated June 13,
1999 to the Board of Directors of Abaous Direct Corporation in the joint proxy
statement/prospectus included in this Registration Statement on Form S-4 of
DoubleClick Inc. (the "Registration Statement"). In giving the foregoing
consent, we do not admit that we come within the category of persons whose
consent is required under Section 7 of the Securities Act of 1933, as amended
(the "Securities Act"), or the rules and regulations promulgated thereunder, nor
do we admit that we are experts with respect to any part of the Registration
Statement within the meaning of the term "experts" as used in the Securities Act
or the rules and regulations promulgated thereunder.

                                          BANCBOSTON ROBERTSON STEPHENS INC.

                                          /s/ BancBoston Robertson Stephens Inc.
                                          San Francisco, CA
                                          October 18, 1999

<PAGE>
                                (Form of Proxy)
                                DOUBLECLICK INC.
          PROXY FOR SPECIAL MEETING OF STOCKHOLDERS NOVEMBER 23, 1999
       (THIS PROXY IS SOLICITED BY THE BOARD OF DIRECTORS OF THE COMPANY)

The undersigned stockholder of DoubleClick Inc. hereby appoints Kevin J.
O'Connor and Kevin P. Ryan, and each of them, with full power of substitution,
proxies to vote the shares of stock which the undersigned could vote if
personally present at the Special Meeting of Stockholders of DoubleClick Inc. to
be held at 8:30 a.m., local time, on November 23, 1999, at 80 Fifth Avenue, 17th
Floor, New York, New York 10011.

1.  APPROVAL OF THE ISSUANCE OF SHARES OF COMMON STOCK PURSUANT TO THE MERGER
    AGREEMENT AMONG DOUBLECLICK INC., ABACUS DIRECT CORPORATION AND ATLANTA
    MERGER CORP.

   / /  FOR               / /  AGAINST               / /  ABSTAIN

2.  GRANTING THE BOARD OF DIRECTORS DISCRETIONARY AUTHORITY TO ADJOURN THE
    SPECIAL MEETING TO SOLICIT ADDITIONAL VOTES FOR APPROVAL OF THE SHARE
    ISSUANCE UNDER THE MERGER AGREEMENT

   / /  FOR               / /  AGAINST               / /  ABSTAIN

3.  APPROVAL OF THE DOUBLECLICK INC. EMPLOYEE STOCK PURCHASE PLAN

   / /  FOR               / /  AGAINST               / /  ABSTAIN

4.  IN THEIR DISCRETION UPON SUCH OTHER MATTERS AS MAY PROPERLY COME BEFORE THE
    MEETING

The Board of Directors recommends a vote FOR each of the proposals.
<PAGE>
   UNLESS OTHERWISE SPECIFIED, THIS PROXY WILL BE VOTED FOR PROPOSAL 1,
    PROPOSAL 2 AND PROPOSAL 3.

                                          Please date and sign exactly as your
                                          name appears on the envelope in which
                                          this material was mailed. If shares
                                          are held jointly, each stockholder
                                          should sign. Executors,
                                          administrators, trustees, etc. should
                                          use full title and, if more than one,
                                          all should sign. If the stockholder is
                                          a corporation, please sign full
                                          corporate name by an authorized
                                          officer. If the stockholder is a
                                          partnership, please sign full
                                          partnership name by an authorized
                                          person.

                                          --------------------------------------
                                          Name(s) of Stockholder

                                          --------------------------------------
                                          Signature(s) of Stockholder

                                          Dated:
                             ---------------------------------------------------

<PAGE>
                                (Form of Proxy)
                           ABACUS DIRECT CORPORATION
          PROXY FOR SPECIAL MEETING OF STOCKHOLDERS NOVEMBER 23, 1999
       (THIS PROXY IS SOLICITED BY THE BOARD OF DIRECTORS OF THE COMPANY)

The undersigned stockholder of Abacus Direct Corporation hereby appoints M.
Anthony White and Carlos E. Sala, and each of them, with full power of
substitution, proxies to vote the shares of stock which the undersigned could
vote if personally present at the Special Meeting of Stockholders of Abacus
Direct Corporation to be held at 9:00 a.m., local time, on November 23, 1999, at
Rihga Royal Hotel, 151 West 54th Street, New York, New York 10019.

1.  APPROVAL AND ADOPTION OF THE MERGER AGREEMENT AMONG DOUBLECLICK INC., ABACUS
    DIRECT CORPORATION AND ATLANTA MERGER CORP.

   / /  FOR               / /  AGAINST               / /  ABSTAIN

2.  GRANTING THE BOARD OF DIRECTORS DISCRETIONARY AUTHORITY TO ADJOURN THE
    SPECIAL MEETING TO SOLICIT ADDITIONAL VOTES FOR APPROVAL OF THE MERGER
    AGREEMENT

   / /  FOR               / /  AGAINST               / /  ABSTAIN

3.  IN THEIR DISCRETION UPON SUCH OTHER MATTERS AS MAY PROPERLY COME BEFORE THE
    MEETING OR ANY ADJOURNMENTS OR POSTPONEMENTS THEREOF

The Board of Directors recommends a vote FOR each of the proposals.
<PAGE>
   UNLESS OTHERWISE SPECIFIED, THIS PROXY WILL BE VOTED FOR PROPOSAL 1 AND
    PROPOSAL 2.

                                          Please date and sign exactly as your
                                          name appears on the envelope in which
                                          this material was mailed. If shares
                                          are held jointly, each stockholder
                                          should sign. Executors,
                                          administrators, trustees, etc. should
                                          use full title and, if more than one,
                                          all should sign. If the stockholder is
                                          a corporation, please sign full
                                          corporate name by an authorized
                                          officer. If the stockholder is a
                                          partnership, please sign full
                                          partnership name by an authorized
                                          person.

                                          --------------------------------------
                                          Name(s) of Stockholder

                                          --------------------------------------
                                          Signature(s) of Stockholder

                                          Dated:
                             ---------------------------------------------------


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