ACI Worldwide Inc. will buy S1 Corp., the companies announced Monday, and combine their global payments and online banking presence.

The deal is a stock and cash blend for about $520 million based on ACI's stock price as of Friday. Both boards have approved the deal, the companies said in a statement.

The price is an increase of 42 cents per share over the offer ACI had made this summer when it launched a bid for S1 after that company had agreed to merge with Fundtech Ltd.

S1's board rejected that ACI offer and said it remained committed to the Fundtech deal, which suddenly ended in mid-September when Fundtech instead was sold to a private equity firm in Chicago.

S1 is an Atlanta-based provider of online banking and payments software with more than 3,000 clients worldwide. It also is owner of PM Systems Corp., a South Carolina-based provider of online banking and security services to about 175 credit unions.

ACI Worldwide has U.S. operations based in Elkhorn, Neb., and said it provides electronic payments to more than 800 financial institutions, retailers and processors globally and financial crime prevention solutions to more than 160 organizations.

The company said it manages more than $12 trillion a day in wholesale payments and more than 90 billion consumer payments a year.

“The combined company will have enhanced scale, breadth and additional capabilities, as well as a complementary suite of products that will better serve the entire spectrum of financial institutions, processors and retailers,” said Philip Heasley, president/CEO of ACI.

“With the significant improvements in the transaction terms and conditions, S1's Board of Directors unanimously concluded that combining with ACI is in the best interests of S1's stockholders, as it provides a substantial premium for their investment and the opportunity to participate further in this powerful combination,” said John Spiegel, chairman of S1.