Kiwibank Migrates to the Postilion Payments Platform

MELBOURNE, Australia and LONDON, May 18, 2009 /PRNewswire-FirstCall/ --
Postilion, a leading global provider of payments software solutions and a
division of S1 Corporation (Nasdaq: SONE), today announced that Kiwibank, the
largest domestically owned bank in New Zealand, has successfully migrated from
an in-house transaction processing system to the open systems based Postilion
platform.

This seven year-old bank, owned by New Zealand Post Ltd., known for its
innovative approach to banking services, is using a range of Postilion
solutions for all of its EFT needs, including the Postilion solution for ATM
owners and the Postilion solution for merchant acquirers. The Postilion
payments platform is now driving Kiwibank's deployment of approximately 300
ATMs and processing transactions from both its cardholders and those from
other banks' customers.

"We had tight project timelines and were extremely impressed with the support
the Postilion team gave us to ensure this significant project was delivered on
schedule," said Murray Soon, ATM Channel Manager - Kiwibank.

"We believe that Kiwibank's choice of Postilion confirms their maturity within
the Australasian payments industry," commented Francois van Schoor, President
of Postilion Payments. "They join a growing number of businesses located
across Asia who are using our solutions and benefiting from improved service
for their customers and offering the opportunity for competitive
differentiation."

About Kiwibank

Kiwibank is a wholly-owned subsidiary of New Zealand Post which is owned by
the Government. Kiwibank was launched in 2002 and provides personal and small
business banking services. It has more than 600,000 customers and operates
profitably. It has the largest network of branches of any bank operating in
New Zealand and 300 ATMs.

About Postilion

Postilion, a division of S1 Corporation (NASDAQ: SONE), is a leading global
provider of payments software solutions used by over 300 banks, card issuers,
merchant acquirers, retailers, and ATM deployers in more than 50 countries.
Together, these customers process over seven billion transactions annually,
originating from more than 100,000 ATMs and 500,000 POS terminals.

Postilion delivers a multi-channel platform that is functionally rich,
extremely flexible, SOA enabled and backed by proven world-class reliability,
availability, security, and performance. With a 15-year track record of
delivering innovative solutions, Postilion can assist in the introduction of
mobile banking, cross-border acquiring, and online payments. Postilion
solutions drive consumer-generated payments with support for EMV, contactless,
prepaid, and gift cards. Postilion offers PCI DSS certified and PA-DSS
compliant solutions. More information is available at www.postilion.com.

About S1 Corporation
S1 Corporation delivers customer interaction software for financial and
payment services and offers unique solution sets for financial institutions,
retailers, and processors under three brand names: Postilion, S1 Enterprise
and FSB Solutions. Additional information about S1 solutions is available at
www.s1.com, www.postilion.com, www.S1enterprise.com, and
www.fsb-solutions.com.

Forward-Looking Statements
This press release contains forward-looking statements within the safe harbor
provisions of the Private Securities Litigation Reform Act. These statements
include statements with respect to our financial condition, results of
operations and business. The words "believes," "expects," "may," "will,"
"should," "projects," "contemplates," "anticipates," "forecasts," "intends" or
similar terminology identify forward-looking statements. These statements are
based on our beliefs as well as assumptions made using information currently
available to us. Because these statements reflect our current views concerning
future events, they involve risks, uncertainties and assumptions. Therefore,
actual results may differ significantly from the results discussed in the
forward-looking statements. The risk factors included in our reports filed
with the Securities and Exchange Commission (and available on our web site at
www.s1.com or the SEC's web site at www.sec.gov) provide examples of risks,
uncertainties and events that may cause our actual results to differ
materially from the expectations we describe in our forward-looking
statements. Except as provided by law, we undertake no obligation to update
any forward-looking statement.

SOURCE S1 Corporation

Cheyanne Atchley, Postilion, +1-512-336-3128, cheyanne.atchley@postilion.com;
Caroline Traylor, Porter Novelli, +1-512-241-2239,
Caroline.Traylor@porternovelli.com, for S1 Corporation