The names, banks and account numbers of up to 40 million credit card holders may have been accessed by an unauthorized user, MasterCard International Inc. said.

The credit card giant said on Friday the security breach involved a computer virus that captured customer data for the purpose of fraud and may have affected holders of all brands of credit cards.

It said the breach was traced to Atlanta-based CardSystems Solutions Inc, which processes credit card and other payments for banks and merchants.

The compromised data did not include addresses or Social Security numbers, said MasterCard spokeswoman Sharon Gamsin. The data that may have been viewed - names, banks and account numbers - could be used to steal funds but not identities.

Gamsin said she did not know how a virus-like computer script that captured customer data got into CardSystems' network, which MasterCard said was infiltrated by an unauthorized individual. Neither company would elaborate.

The FBI was investigating.

The incident was the latest in a series of security breaches affecting valuable consumer data at major financial institutions and data brokers in an increasingly database-driven world.

The breach appears to be the largest yet involving financial data, said David Sobel, general counsel at the Electronic Privacy Information Centre.

"The steady stream of these disclosures shows the pressing need for regulation of the industry both in terms of limitation in the amount of personal information that companies collect and also liability when these kinds of disclosures occur," Sobel said.

MasterCard, which said about 14 million of its own cards were exposed, first announced the breach in a news release on Friday afternoon, saying it was notifying its card-issuing banks of the problem.

However, CardSystems said later on Friday in a statement vetted by the FBI that it first learned of a potential breach on May 22. It said it was told by the FBI not to release any information to the public. The company said it was surprised by MasterCard's decision to go public.

Under federal law, credit card holders are liable for no more than US$50 of unauthorized charges, and many card issuers including MasterCard will even waive the US$50.

CardSystems processes less than 0.5 per cent of American Express' domestic transactions, said company spokeswoman Judy Tenzer. She said a small number of its cardholders were affected, though she did not have an exact figure.

Discover Financial Services Inc. said it was aware of the situation and would not say whether any of its cards were involved.

Source: China Daily