S1 Corporation Agrees to Settle Shareholder Litigation

NORCROSS, Ga., Oct. 25, 2011 (GLOBE NEWSWIRE) -- S1 Corporation (Nasdaq:SONE),
a leading global provider of payments and financial services software
solutions, announced today that it and other named defendants have reached an
agreement in principle with plaintiffs to settle the consolidated class action
lawsuit captioned In re S1 Corporation Shareholders Litigation. This lawsuit
relates to the now-terminated merger with Fundtech Ltd. and the proposed
acquisition of the Company by ACI Worldwide, Inc. ("ACI").

Pursuant to this agreement, the Company has filed an amendment to its
Solicitation/Recommendation Statement on Schedule 14D-9 with the Securities
and Exchange Commission, which can be accessed free of charge at the SEC's
website at www.sec.gov, or the Company's website, www.s1.com. The amended
Schedule 14D-9 contains certain additional disclosures the Company agreed to
make in connection with the settlement of the lawsuit, although the Company
has not admitted in any way that those disclosures are material or are
otherwise required by law. The settlement will not affect the offer price to
be paid in the current exchange offer by a subsidiary of ACI or the merger
consideration the Company's stockholders would be entitled to receive pursuant
to the terms of the previously announced Transaction Agreement, dated as of
October 3, 2011, by and among the Company, ACI and a subsidiary of ACI.

About S1 Corporation

Leading banks, credit unions, retailers, and processors need technology that
adapts to the complex and challenging needs of their businesses. These
organizations want solutions that can respond quickly to changes in the
marketplace and help grow their businesses. For more than 20 years, S1
Corporation (Nasdaq:SONE) has been a leader in developing software products
that offer flexibility and reliability. Over 3,000 organizations worldwide
depend on S1 for payments, online banking, mobile banking, voice banking,
branch banking and lending solutions that deliver a competitive advantage.
More information is available at www.s1.com.

Forward Looking Statements

Certain statements in this letter may constitute "forward-looking statements"
within the meaning of the Private Securities Litigation Reform Act of 1995.
Such statements include, but are not limited to, those regarding any
transaction with ACI Worldwide, Inc., the settlement referred to herein and
other statements that are not historical facts. These statements involve risks
and uncertainties including those detailed in S1's Annual Reports on Form 10-K
and other filings with the Securities and Exchange Commission ("SEC"). Should
one or more of these risks or uncertainties materialize, or should underlying
assumptions prove incorrect, actual outcomes may vary materially from those
forecasted or expected. S1 disclaims any intention or obligation to update
publicly or revise such statements, whether as a result of new information,
future events or otherwise.

Additional Information and Where to Find It

S1 Corporation has filed a Solicitation/Recommendation Statement on Schedule
14D-9, as amended, with the SEC. INVESTORS AND STOCKHOLDERS ARE URGED TO READ
THAT STATEMENT AND OTHER MATERIALS FILED WITH THE SEC BY S1 BECAUSE THEY
CONTAIN IMPORTANT INFORMATION.S1 stockholders and other interested parties
may obtain, free of charge, copies of S1's Schedule14D-9, as amended, and
other documents filed by S1 with the SEC at the SEC's website at
http://www.sec.gov.In addition free copies of the documents filed by S1 with
the SEC with respect to the exchange offer may be obtained by contacting S1's
Investor Relations at (404) 923-3500 or by accessing S1's investor relations
website at www.s1.com.

CONTACT: S1 Corporation
         Paul M. Parrish
         Chief Financial Officer
         404.923.3500
         paul.parrish@s1.com