<TABLE> <S> <C>

<PAGE>
 
<ARTICLE> 5
<RESTATED> 
<MULTIPLIER> 1,000
       
<S>                             <C>                     <C>                        <C>                    
<PERIOD-TYPE>                   3-MOS                   6-MOS                      9-MOS                  
<FISCAL-YEAR-END>                          SEP-30-1998             SEP-30-1998                SEP-30-1998 
<PERIOD-START>                             OCT-01-1997             OCT-01-1997                OCT-01-1997 
<PERIOD-END>                               DEC-31-1997             MAR-31-1998                JUN-30-1998 
<CASH>                                          33,351                  46,133                     75,047 
<SECURITIES>                                    51,128                  46,171                     31,060 
<RECEIVABLES>                                   13,721                  15,975                     15,150 
<ALLOWANCES>                                     1,309                   1,681                      1,923 
<INVENTORY>                                      1,181                   1,434                      1,085 
<CURRENT-ASSETS>                               107,178                 119,086                    132,679 
<PP&E>                                          15,594                  17,133                     19,047 
<DEPRECIATION>                                   6,405                   7,736                      9,226 
<TOTAL-ASSETS>                                 123,081                 136,037                    153,048 
<CURRENT-LIABILITIES>                           35,404                  35,094                     39,938 
<BONDS>                                              0                       0                          0 
<PREFERRED-MANDATORY>                                0                       0                          0 
<PREFERRED>                                          0                       0                          0 
<COMMON>                                        57,832                  68,217                     71,973 
<OTHER-SE>                                           0                       0                          0 
<TOTAL-LIABILITY-AND-EQUITY>                   123,081                 136,037                    153,048 
<SALES>                                         37,497                  77,586                    121,772 
<TOTAL-REVENUES>                                37,497                  77,586                    121,772 
<CGS>                                            3,392                   7,029                     11,169 
<TOTAL-COSTS>                                    3,392                   7,029                     11,169 
<OTHER-EXPENSES>                                25,326                  58,713                     88,700 
<LOSS-PROVISION>                                     0                       0                          0 
<INTEREST-EXPENSE>                                  23                      46                         97 
<INCOME-PRETAX>                                  9,892                  14,316                     25,578 
<INCOME-TAX>                                     2,514                   3,612                      6,425 
<INCOME-CONTINUING>                              7,378                  10,704                     19,153 
<DISCONTINUED>                                       0                       0                          0 
<EXTRAORDINARY>                                      0                       0                          0 
<CHANGES>                                            0                       0                          0 
<NET-INCOME>                                     7,378                  10,704                     19,153 
<EPS-PRIMARY>                                     0.26                    0.37                       0.65 
<EPS-DILUTED>                                     0.24                    0.35                       0.61 
        

</TABLE>