The announcement by S1 Corp. that it received an unsolicited takeover offer from ACI Worldwide, Inc to acquire S1 Corporation for $9.50 per share prompted an investigation on behalf of investors of S1 Corporation (NASDAQ:SONE) concerning whether the buyout offer and the process are unfair to investors of S1 Corp. (SONE), and whether certain of its officers and directors or others breached their fiduciary duties owed investors in S1 (NASDAQ:SONE) shares.

The investigation by a law firm concerns whether the S1 Corporation, certain of its officers and directors, and/or others breached their fiduciary duties owed to S1 Corp. (NASDAQ:SONE) investors in connection with the proposed takeover.

On June 27, 2011, S1 Corporation (Nasdaq:SONE) and Fundtech Ltd. (Nasdaq:FNDT) announced that they have entered into an agreement to combine businesses through a stock-for-stock merger. Under the terms of the proposed transaction, Fundtech shareholders will receive 2.72 shares of S1 common stock for each Fundtech ordinary share they own.

Then on July 26, 2011, S1 Corporation (Nasdaq:SONE) announced that it has received a letter dated July 26, 2011 from ACI Worldwide, Inc. (Nasdaq:ACIW) outlining an unsolicited proposal to acquire S1 Corporation for $9.50 per share in a mix of cash and common stock of ACI.

Following the proposal to takeover S1 Corporation shares of S1 Corp. (NASDAQ:SONE) jumped from a close of $7.13 per share on July 25, 2011 to a high of $9.43 on July 26,2011.

However, at least one analyst has set the high target price for S1 Corporation NASDAQ SONE stock at $13.00 per share.

Therefore the investigation concerns whether the S1 Corp. Board of Directors undertook an adequate and in particular breached their fiduciary duties to the S1 Corporation (NASDAQ:SONE) shareholder by failing to adequately shop the Company before entering into the transaction. The investigation concerns also whether ACI Worldwide, Inc would underpay for NASDAQ:SONE shares, thus unlawfully harming S1 stockholders.

S1 Corps financial performance increased lately. Even though S1 Corps annual Total Revenue increased only slightly from $204.93million in 2007 to $209.09million in 2010 and its latest annual Revenue fell compared to its Total Revenue of $228.55million in 2008 and 238.93million in 2009, S1 Corporation was able to report an increased first quarter Revenue of $57.84million for the first quarter in 2011, compared to a first quarter Revenue of $51.16million a year earlier. Additionally S1 Corporation was able to pull out of its last year first quarter Net Loss of $1.06milion and report for the first quarter in 2011 a Net Income of $0.68million.

A potential securities class action lawsuit would seek to maximize the amount of money and information S1 (NASDAQ:SONE) shareholders would receive in a buyout, so the law firm.