ACI Worldwide Inc, a global provider of electronic payments software to the banking and retail industry, today agreed to buy financial services provider S1 Corp in a $540 million cash-and-stock deal.

Omaha, Nebraska-based ACI provides electronic payments software to more than 800 financial institutions, retailers and processors around the world. On an average, ACI claims that its software manages more than $12 trillion in wholesale payments for more than 160 organisations worldwide daily.

Nineteen of the world's top 20 banks, 5 of the top 10 US retailers and 6 of the leading 25 global retailers use ACI payments software. Its software also helps to protect its customers from financial crime.

For more than 20 years, Georgia-based S1 has been developing software solutions on an open platform to over 3,000 organisations in more than 75 countries related to payments, online banking, and branch banking.

ACI will pay $9.50 per S1 share, a premium of 33 per cent to S1's stock close on 25 July. The deal consists of 40 per cent in ACI stock and 60 per cent in cash.

The acquisition of S1 would support ACI's position as the leading provider of the most unified payments solution to serve retail banking, wholesale banking, processors and retailers.

"We believe a combination with S1 would provide ACI with enhanced scale, breadth and additional capabilities to compete more effectively and profitably in the global marketplace," said Philip Heasley, president and CEO of ACI.

"ACI and S1 have complementary products and customer bases, and together would better serve the entire spectrum of financial institutions, processors and retailers.

The transaction is also expected to create significant financial benefits, including considerable cost savings and cross-selling opportunities beyond what either company could achieve on its own," he added.