VISA, THE world’s largest payment processor, warned of a potential breach at a third-party credit and debit card processor that has affected account information from “all major credit card brands”.

MasterCard, its smaller rival, confirmed yesterday it was investigating a breach at a third-party processor that may have compromised cardholder account data.

Details on how the breach occurred and the extent of the possible effects on customers were sparse, as Visa and MasterCard both declined to comment on how many cardholders may have been affected. Each company said its systems had not been compromised.

Shares in Global Payments, an Atlanta, Georgia-based company that provides payment processing servicers, were suspended from trading on the New York Stock Exchange.

The suspension came after a fall in the stock in New York trading and was pending an announcement, the exchange said. Officials at Global Payments were unavailable to comment, but a person familiar with the situation said the breach occurred at the processor.

MasterCard has begun informing banks and financial companies that issue their branded cards of a potential breach, a person familiar with the matter said. Visa said it “has provided payment card issuers with the affected account numbers so they can take steps to protect customers through independent fraud monitoring and, if needed, reissuing cards”.

George Ogilvie, a spokesman for the US Secret Service, said the agency was investigating the breach.

MasterCard and Visa process transactions on their networks between banks and institutions that issue their cards and those that work with merchants accepting them.

MasterCard said: “We continue to both monitor this event and take steps to safeguard account information. If cardholders have any concerns about their individual accounts, they should contact their issuing financial institution.”

Visa said its cardholders were “protected against fraudulent purchases”.

People familiar with investigations of the breach said lending banks were working with payment processors, and were preparing to field customer inquiries about suspicious charges on their cards.

Officials for Discover and American Express were not available to comment on whether their cardholders had been affected. Citigroup, Bank of America and JPMorgan Chase declined to comment on the breach.