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Analysts said MasterCard and Visa are unlikely to face costs from the breach, but MasterCard shares fell 1.8 per cent to close at $420.54. Image Credit: Bloomberg

New York: The US Secret Service is investigating a major cyber intrusion at an Atlanta-based payment processor that could expose millions of MasterCard, Visa, American Express and Discover cardholders to fraudulent charges.

Processor Global Payments Inc said on Friday it had found "unauthorised access" into its system early in March and notified law enforcement and financial institutions.

Payment network operators MasterCard, Visa, American Express and Discover Financial Services confirmed they were affected, along with banks and other franchises that issue cards bearing their logos.

A spokesman for the Secret Service said the agency is leading investigations into the case but declined to give any details.

Though Global Payments is far from a household name, middlemen such as the company are prized targets for hackers because of the vast amount of sensitive financial information they handle.

The company's stock fell more than 9 per cent on the news before trading was halted. It said it would discuss the breach in a phone call for investors tomorrow.

It was not immediately clear how Global Payments was penetrated or how many accounts were exposed. Consumers who detect fraud usually can be reimbursed. That leaves merchants on the hook financially, though they could file claims against Global Payments.

Analysts said MasterCard and Visa are unlikely to face costs from the breach, but MasterCard shares fell 1.8 per cent to close at $420.54 (Dh1,543.38) and Visa shares dropped 0.8 per cent to $118.

At risk

The security breach is just the latest in a long string of incidents that have put the personal information of millions of credit and debit cardholders at risk.

Individual banks and processors said they had not yet determined the full extent of the breach, but the blog Krebs on Security, which first reported the breach, said it was "massive" and could affect more than 10 million cardholders.

Some industry experts suggested the figure might be much lower, perhaps on the order of tens of thousands. Bernstein Research analyst Rod Bourgeois noted that Global Payments is a relatively small player in the transactions services industry, servicing 800,000 merchants with a 3.5 per cent market share. By contrast, the largest competitor, First Data, services millions of merchants, with 22.6 per cent of the market.

Monitoring accounts

JPMorgan Chase & Co, as well as American Express and Discover, which issue their own cards, said they are monitoring customers' accounts and would issue new cards to anyone whose information may have been compromised.

Citigroup said it has been notified by processors of the breach. Bank of America Corp declined to comment on the matter and Wells Fargo & Co said it was too early to comment on the impact.

Banks and processors emphasised customers would not be held liable for any fraudulent charges that may occur.

Michael Simonsen, chief executive of real-estate research company Altos Research, said he may have been a victim.

Simonsen said he was contacted by Bank of America last week about his Visa card.