ST. PETERSBURG, Fla. — A sophisticated Sept. 20 phishing attack targeted credit union cardholders by masquerading as a site sponsored by Card Services for Credit Unions, the association of credit unions that processes their card transactions with Fidelity National Information Services.

Sue Chrzan, spokesman for the association, said employees became aware of the problem early in the morning when their desk computers were extraordinarily slow. Information technology specialists at CSCU said they were alerted to the problem because their servers had to process thousands of e-mails being returned to a bogus CSCU address.

"We acted quickly to get communications out to our member credit unions and to redirect the images on the phishing site to warnings," said Chrzan. She said the association had contacted Fidelity National and put into place a program Fidelity has to swiftly shut down these sorts of attacks when they occur.