ATLANTA — CheckFree Corp. has completed its $245 million acquisition of Corillian, giving the combined organization an end-user base of more than 40 million online bankers and 250,000 small businesses.

CheckFree already provided processing of more than two-thirds of all ACH transactions in the United States, the company says, and now serves more than 31 million bill presentment and payment customers as well.

The combined organization also now serves 21 of the 25 largest financial institutions in the country, the company says. Oregon-based Corillian made its name providing online banking and leading-edge phishing detection and other fraud solutions to banks and large credit unions.

The combined company says it plans to deliver highly flexible deployment options to help manage total cost of ownership for financial institutions of any size.

“Corillian shares our vision of optimizing the online financial services experience by offering broader payment capabilities, integrated self-service tools and helping financial institutions generate revenues through the online channel,” said Pete Kight, CheckFree chairman and chief executive officer.