<TABLE> <S> <C>

<PAGE>
<ARTICLE> 5
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM SIEBEL
SYSTEMS, INC. QUARTERLY REPORT ON FORM 10-Q FOR THE QUARTERS ENDED SEPTEMBER 30,
1997 AND 1998 IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH FINANCIAL
STATEMENTS. THE SUMMARY FINANCIAL INFORMATION FOR THE QUARTER ENDED SEPTEMBER
30, 1997 HAS BEEN RESTATED TO REFLECT THE EFFECT OF THE POOLING OF INTERESTS
BETWEEN SIEBEL SYSTEMS, INC. AND SCOPUS TECHNOLOGY, INC., WHICH OCCURRED ON MAY 
18, 1998.
</LEGEND>
<RESTATED> 
<MULTIPLIER> 1,000
       
<S>                             <C>                     <C>
<PERIOD-TYPE>                   9-MOS                   9-MOS
<FISCAL-YEAR-END>                          DEC-31-1997             DEC-31-1998
<PERIOD-START>                             JAN-01-1997             JAN-01-1998
<PERIOD-END>                               SEP-30-1997             SEP-30-1998
<CASH>                                          57,436                 105,700
<SECURITIES>                                    85,605                 123,476
<RECEIVABLES>                                   59,443                 107,849
<ALLOWANCES>                                         0                       0
<INVENTORY>                                          0                       0
<CURRENT-ASSETS>                               211,743                 349,836
<PP&E>                                          22,114                  30,168
<DEPRECIATION>                                       0                       0
<TOTAL-ASSETS>                                 240,415                 385,701
<CURRENT-LIABILITIES>                           48,453                 129,478
<BONDS>                                              0                       0
<PREFERRED-MANDATORY>                                0                       0
<PREFERRED>                                          0                       0
<COMMON>                                       164,045                 220,597
<OTHER-SE>                                      27,712                  35,464
<TOTAL-LIABILITY-AND-EQUITY>                   240,415                 385,701
<SALES>                                        104,435                 200,567
<TOTAL-REVENUES>                               138,397                 268,382
<CGS>                                            2,843                   4,295
<TOTAL-COSTS>                                   22,497                  47,025
<OTHER-EXPENSES>                               100,013                 184,249
<LOSS-PROVISION>                                     0                       0
<INTEREST-EXPENSE>                                   0                       0
<INCOME-PRETAX>                                 19,840                  41,584
<INCOME-TAX>                                     7,543                  18,583
<INCOME-CONTINUING>                             12,297                  23,001
<DISCONTINUED>                                       0                       0
<EXTRAORDINARY>                                      0                       0
<CHANGES>                                            0                       0
<NET-INCOME>                                    12,297                  23,001
<EPS-PRIMARY>                                     0.15                    0.26
<EPS-DILUTED>                                     0.13                    0.23
        

</TABLE>