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NEW YORK - A computer hacker may have accessed more than 40 million credit card accounts in what would be the largest in a series of recent security breaches involving consumer data, officials said this weekend.

MasterCard International said on Friday that the breach had been traced to Atlanta-based CardSystems Solutions, which processes credit card and other payments for banks and merchants. All brands of credit cards could be affected.

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 the 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.

MasterCard said 14 million of its customers may have been exposed to fraud. A spokeswoman for American Express said that a small number of its cardholders were affected, but would not give an exact number.

Discover Financial Services wouldn't say whether its customers were affected. Visa USA and a large issuer of cards, MBNA Corp., did not return calls for comment.

Latest in a series of lapses

The incident was the latest in a series of security lapses affecting consumer information. The breach appears to be the largest yet involving financial data, said David Sobel, general counsel at the Electronic Privacy Information Center in Washington.

"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," he said.

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

Other companies that have been hit by security lapses recently include Citigroup, Bank of America and DSW Shoe Warehouse. Federal lawmakers have responded by drawing up legislation designed to better protect consumer privacy.

MasterCard announced the breach in a news release Friday, saying it was notifying its card-issuing banks of the problem.

CardSystems then released its own statement, saying it first learned of a potential breach on May 22. The company said it was told by the FBI not to release any information to the public; its statement Friday had been veted by the agency.

"We were absolutely blindsided" by MasterCard's announcement, CardSystems' chief financial officer, Michael Brady, said.

CardSystems, which has a processing center in Tempe, Arizona, has been in business for more than 15 years and handles transactions for more than 115,000 small to mid-sized businesses, according to the company's Web site. The company says it processes transactions worth more than $15 billion annually.

Sobel said the fact that the latest breach involved a third party "indicates that this is a shadowy industry where the consumer never really knows who is going to be handling and using their personal information."

Earlier this month, Citigroup said UPS lost computer tapes containing sensitive information from 3.9 million customers of CitiFinancial, which provides loans.

There have also been breaches involving other kinds of sensitive data.

ChoicePoint Inc. said in February that thieves using stolen identities had created 50 dummy businesses that pulled data including names, addresses and Social Security numbers on as many as 145,000 people.