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                          [S1 CORPORATION LETTERHEAD]


                                     
CONTACTS:
Sam Perkins                             Julie Carlyle
Vice President, Investor Relations          S1 Public Relations
S1 Corporation                              404.812.6646
404-812-6671                                julie.carlyle@s1.com
sam.perkins@s1.com


S1 Corporation Comments on Expected Fourth Quarter Results

ATLANTA, January 18, 2001 - S1 Corporation (NASDAQ: SONE), a leading global
provider of eFinance solutions and services, today said that it would likely
report fourth quarter revenue between $60 and $60.5 million and an EBITDA loss
of between $25 and $28 million (EBITDA loss of $0.44-$0.50 per share). For the
fourth quarter, S1 expects to report a net loss of between $318 and $371 million
(loss of $5.64 to $6.58 per share).

"The fourth quarter results, while disappointing, are the result of our efforts
to introduce greater operational efficiencies into the business and more
effectively position ourselves and our customers for long-term success in this
rapidly evolving market," said Jaime Ellertson, chief executive officer, S1
Corporation. "We believe the actions taken in the fourth quarter did not have a
material impact on cash usage, will improve our ability to meet our strategic
business plan and drive S1 to EBITDA breakeven during 2001."

Mr. Ellertson will host a conference call this morning at 9:00 a.m. Eastern
Time. The conference call will be accessible through the Internet at the
following URL: http://www.vcall.com/NASApp/Vcall/EventPage?ID=63961. The call
will be recorded and available for play back by noon, Eastern Time, by dialing 1
(888) 203-1112 (US & Canada) 1 (719) 457-0820 (International). The access code
is 581104. The replay will be active until midnight Eastern Time on January 25,
2001.

About S1 Corporation
               S1 (NASDAQ:SONE), the pioneer of Internet banking, is a leading
global provider of innovative eFinance solutions and services that are centered
on banking, brokerage and insurance. S1 is enabling financial service providers
to create a complete Enterprise eFinance Experience(TM) by delivering the tools
necessary to meet the evolving demands of their customers across various lines
of businesses, market segments and delivery channels. Through its Open eFinance


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Architecture(TM), S1 offers a broad range of applications that empower financial
institutions to increase revenue, strengthen customer relationships and gain
competitive advantage. Additionally, through the Company's professional services
organization, S1 applications can be implemented in-house or hosted in an S1
Data Center. Additional information about S1 is available at http://www.s1.com.


Forward-Looking Statements
               This press release includes statements and other matters which
are forward-looking and subject to a number of risks and uncertainties that
could cause actual results to differ materially from expectations. The
statements contained in this release that are forward-looking are based on
current expectations and are subject to risks and uncertainties that could cause
actual results to differ materially from the results contemplated by the
forward-looking statements. These risks and uncertainties include, but are in no
way limited to:

- -       the possibility that actual fourth quarter results will differ from
        these preliminary estimates

- -       the possibility that the anticipated benefits from our acquisition
        transactions will not be fully realized;

- -       the possibility that costs or difficulties related to our integration of
        acquisitions will be greater than expected;

- -       our dependence on the timely development, introduction and customers
        acceptance of new internet services;

- -       rapidly changing technology and shifting demand requirements and
        internet usage patterns;

- -       other risks and uncertainties, including the impact of competitive
        services, products and prices, the unsettled conditions in the internet
        and other high-technology industries and the ability to attract and
        retain key personnel; and

- -       other risk factors as may be detailed from time to time in our public
        announcements and filings with the SEC, including the Company's annual
        report on Form 10-K for the year ended December 31, 1999.

Except as required by law, S1 will not update forward looking statements over
the course of future periods.

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                          3390 Peachtree Rd., Ste. 1700

                             Atlanta, Georgia 30326