Of those exposed accounts, about 13.9 million are for MasterCard-branded cards, the company said in a statement. Some 20 million Visa-branded cards may have been affected and the remaining accounts were other brands, including American Express and Discover.MasterCard and Visa both say they have notified their member banks of the specific accounts involved so the banks can take action to protect cardholders.
"In sheer numbers, this is probably one of the largest data security breaches," said James Van Dyke, principal analyst at Javelin Strategy & Research in Pleasanton, Calif.
In what could be the largest data security breach in the world to date, information on 40 million credit card accounts might have been stolen.
The massive breach follows several high-profile data loss incidents that potentially exposed American consumers to identity theft. The incident also comes as the public expresses increasing concern over identity theft.
The breach occurred at CardSystems Solutions in Tucson, Ariz., a third-party processor of payment data, according to a MasterCard statement. An intruder was able to use security vulnerabilities to infiltrate the CardSystems network and access the cardholder data, MasterCard said.
CardSystems is one of several companies that process transactions for banks and merchants. The security breach at the company was discovered using tools that monitor for credit card fraud, MasterCard said.
Though credit card numbers were compromised, the cards themselves do not hold social security numbers or dates of birth, MasterCard said. This information could be used for credit card fraud, but not to steal identities.
Leslie Sutton, a spokeswoman for credit card company Discover, said the company is aware of the security breach and is working with law enforcement to investigate it. She noted that Discover Card holders would not be liable for any fraudulent transactions, should they occur.
Visa issued a statement saying it knows of the data security breach and is working with authorities and banks to monitor and prevent fraud. As with MasterCard and Discover, Visa noted that card users are not responsible for fraudulent transactions.
American Express could not immediately be reached for comment.
The credit card theft possibly occurred late last month, according to CardSystems. In a statement issued late Friday, the company said that it identified a "potential security incident" on Sunday, May 22 and called in the FBI the next day. Visa and MasterCard were notified as well, CardSystems said.
Since the breach, CardSystems has undergone a security audit and is changing its security procedures as a result, it said.
Tide of leaks
The breach follows several high-profile data loss incidents that potentially exposed American consumers to identity theft. Last week, CitiFinancial said tapes containing unencrypted information on 3.9 million customers were lost by the United Parcel Service while in transit to a credit bureau. CitiFinancial is the consumer finance subsidiary of Citigroup.
In past months, data leaks have been reported byand Wachovia, data brokers and LexisNexis, and the University of California at Berkeley and .
Two recent surveys have highlighted growing worries about data protection. On Wednesday, the Cyber Security Industry Alliance reported that 97 percent of theit polled said identity theft was a problem that needs addressing, and 64 percent wanted the government to do more to protect computer security.
In addition, a study commissioned by Adobe Systems and RSA Securitythat eight out of 10 "senior-level professionals" in Washington, D.C., thought that lawmakers weren't doing enough to keep consumer data safe.
In the United States, MasterCard cardholders are protected against unauthorized transactions on their accounts. If cardholders believe their cards were used fraudulently, they should contact their bank, MasterCard said.
Credit card holders should monitor their accounts online for fraud, Javelin Strategy & Research's Van Dyke advised. "For identity fraud, the individual cardholder is most likely the first who will discover it," he said.
MasterCard is working with banks, CardSystems and law enforcement agencies on the security break-in.
CardSystems has taken steps to improve the security of its system, MasterCard said. Still, the credit card company has given the data processor an undisclosed deadline to demonstrate that its systems are now secure, it said.