<TABLE> <S> <C>
<ARTICLE> 5
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM THE
CONSOLIDATED FINANCIAL STATEMENTS OF INTERNET SECURITY SYSTEMS, INC. AS OF AND
FOR THE NINE MONTHS ENDED SEPTEMBER 30, 2000 AND IS QUALIFIED IN ITS ENTIRETY
BY REFERENCE TO SUCH FINANCIAL STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000
<CURRENCY> U.S. DOLLARS
<S> <C>
<PERIOD-TYPE> 9-MOS
<FISCAL-YEAR-END> DEC-31-2000
<PERIOD-START> JAN-01-2000
<PERIOD-END> SEP-30-2000
<EXCHANGE-RATE> 1
<CASH> 28,593
<SECURITIES> 110,670
<RECEIVABLES> 43,523
<ALLOWANCES> 999
<INVENTORY> 1,392
<CURRENT-ASSETS> 187,003
<PP&E> 25,686
<DEPRECIATION> 11,702
<TOTAL-ASSETS> 221,534
<CURRENT-LIABILITIES> 43,682
<BONDS> 0
0
0
<COMMON> 42
<OTHER-SE> 177,566
<TOTAL-LIABILITY-AND-EQUITY> 221,534
<SALES> 0
<TOTAL-REVENUES> 135,295
<CGS> 0
<TOTAL-COSTS> 122,190
<OTHER-EXPENSES> 494
<LOSS-PROVISION> 0
<INTEREST-EXPENSE> 0
<INCOME-PRETAX> 18,802
<INCOME-TAX> 6,796
<INCOME-CONTINUING> 12,006
<DISCONTINUED> 0
<EXTRAORDINARY> 0
<CHANGES> 0
<NET-INCOME> 12,006
<EPS-BASIC> 0.29
<EPS-DILUTED> 0.27
</TABLE>