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                                                                     EXHIBIT 21

                                   EXHIBIT A

                 RELEVANT SUBSIDIARIES OF PARENT HOLDING COMPANY

PART A: TCW ENTITIES

PARENT HOLDING COMPANY:

     The TCW Group, Inc.

     Robert Day (an individual who may be deemed to control The TCW Group, Inc.)


RELEVANT SUBSIDIARIES THAT ARE PERSONS DESCRIBED IN RULE 13d-1(b):

     (i)   TCW Asset Management Company, a California corporation and an
           Investment Adviser registered under Section 203 of the Investment
           Advisers Act of 1940.

     (ii)  TCW Investment Management Company, fka: TCW Funds Management, Inc., a
           California corporation and an Investment Adviser registered under
           Section 203 of the Investment Advisers Act of 1940.

Note:  No Class A Common Stock of McAfee.Com Corp. is held directly by The TCW
       Group, Inc. Other than the indirect holdings of The TCW Group, Inc., no
       Class A Common Stock of McAfee.Com Corp. is held directly or indirectly
       by Robert Day, an individual who may be deemed to control The TCW Group,
       Inc.

PART B: NON TCW ENTITIES

PARENT HOLDING COMPANY:

     Robert Day (an individual who may be deemed to control the entities
     described below which are not subsidiaries of The TCW Group, Inc.)

RELEVANT SUBSIDIARIES THAT ARE PERSONS DESCRIBED IN RULE 13d-1(b):

     Oakmont Corporation, a California corporation and an Investment Adviser
     registered under Section 203 of the Investment Advisers Act of 1940.


                                      A-1



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