S1 Corporation Board Urges Stockholders to Take no Action at This Time in Response to ACI Exchange Offer

S1 Corporation SONE today responded to the unsolicited and conditional exchange offer announced on August 30, 2011 by ACI Worldwide, Inc. ACIW. Subject to the terms and various conditions set forth in the exchange offer, ACI seeks to acquire each outstanding share of S1 common stock for an election between cash and ACI shares, subject to proration.