American Express Co. said today it would buy Accertify Inc., a company that sells fraud prevention services to online retailers and other merchants.  Amex expects to pay $150 million for the company, and to close the deal by the end of the year.

Accertify provides fraud prevention to 17 businesses in the Internet Retailer Top 500 Guide, an Accertify spokeswoman says.  Accertify lists among its clients such retailers as Blockbuster Inc., No. 34 in The Guide; 1-800-Flowers.com Inc., No. 40; BarnesandNoble.com Inc., No 42; Urban Outfitters, No. 53; and Gilt Groupe, No. 140.

Accertify, started by former executives of online travel site Orbitz, went into business in 2007 and provides fraud prevention software that helps secure transactions conducted via PayPal and the major payment card networks against which American Express competes. American Express says the acquisition will enable it to provide fraud prevention services to merchants on transactions across all networks. Merchants also outsource fraud prevention tasks to Accertify.

“Merchants are interested in fraud tools that cover every aspect of the payment process and we’re pleased that we will now be able to deliver an industry-leading solution to them,” says Bill Glenn, president of American Express Global Merchant Services. “While we already provide innovative fraud services for American Express transactions, merchants increasingly want single source platforms to address all types of transactions, regardless of the payment brand.”

Accertify president Jeff Liesendahl will continue in that job, Amex says. “Becoming part of American Express will enable us to build on our success by scaling our business, providing even more merchant benefits and extending our global presence,” he says.

Accertify will operate as a wholly owned subsidiary of the payment card network.

“Accertify is a very promising and leading online retail fraud prevention vendor,” says Avivah Litan, senior analyst at Gartner Research. “It’s good news for Amex to acquire such leading technology but hopefully Accertify will retain its independence because retailer fraud prevention needs to be card brand neutral.”