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Exhibit 99.1

CERTIFICATION OF CHIEF EXECUTIVE OFFICER AND CHIEF FINANCIAL OFFICER
PURSUANT TO
18 U.S.C. SECTION 1350,
AS ADOPTED PURSUANT TO
SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

        I, Peter M. Caswell, certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that the Quarterly Report of Advent Software, Inc. on Form 10-Q for the quarterly period ended September 30, 2002 fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934 and that information contained in such Form 10-Q fairly presents in all material respects the financial condition and results of operations of Advent Software, Inc.

By:	/s/  PETER M. CASWELL
Name:	Peter M. Caswell
Title:	Chief Executive Officer and President

         I, Irv H. Lichtenwald, certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that the Quarterly Report of Advent Software, Inc. on Form 10-Q for the quarterly period ended September 30, 2002 fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934 and that information contained in such 10-Q fairly presents in all material respects the financial condition and results of operations of Advent Software, Inc.

By:	/s/  IRV H. LICHTENWALD
Name:	Irv H. Lichtenwald
Title:	Executive Vice President, Chief Financial Officer and Secretary

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Exhibit 99.1

CERTIFICATION OF CHIEF EXECUTIVE OFFICER AND CHIEF FINANCIAL OFFICER PURSUANT TO 18 U.S.C. SECTION 1350, AS ADOPTED PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002