Banks in the United Arab Emirates are struggling to resolve a security breach after it emerged that hackers used counterfeit bank and credit cards to steal funds from customers’ accounts.

The lenders declined to say how much money had been stolen or how many accounts were skimmed, but an initial investigation by the banks indicated that cash machines were rigged with devices that stole customers’ PINs as they made withdrawals.

Suvo Sarkar, general manager of retail banking for Emirates NBD, one of the nation’s largest lenders, said: “We don’t really know how this happened.”

However, one industry source suggested that the problem could be internal and more widespread. “The fact that the stolen numbers appear to have been stolen randomly suggests the banks themselves were somehow breached.”

Mr Sakar said that the hackers were part of an international network, with most of the fraudulent transactions originating from more than 20 countries outside the UAE.

The banks have tried to prevent further losses by sending text messages urging their customers to change their PINs, and promising to reimburse them for any funds stolen from their accounts.

HSBC, Citibank, Lloyds TSB, National Bank of Abu Dhabi and Emirates NBD have issued statements saying that the problem is under control, but some customers remain unconvinced and believe that the banks failed to protect them.

Some of the lenders moved to block the accounts of clients who have failed to change their PINs, causing chaos.

Dubai Bank said that it had temporarily blocked international access to its cash machines after 42 of its customers’ accounts were breached.

Wael Jundi, a corporate adviser with SinoGulf, an investment fund, said that he was considering closing his account at HSBC: “This is absolutely ridiculous. The banks have broken their trust with the customer and we still don’t have any answers as to why this happened in the first place.”

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