However, banks have played down consumer fears, claiming that most victims of the credit card infraction had already been identified and issued with replacement cards earlier this year.

About 50,000 MasterCard and 77,000 Visa card holders in Australia are among the 40 million credit card holders worldwide that may have had their personal data stolen from a card processing company in the US.

News of the scandal, possibly the largest of its kind in the US, broke on June 17 when it emerged that Arizona-based CardSystems Solutions had improperly retained information on 40 million customers.

CardSystems’ chief John Perry told the New York Times newspaper data on about 200,000 customers had actually been stolen.

Mr Perry said the sensitive data in question was no longer stored on files.

Australians most likely to be affected are those who made transactions either while travelling in America or making online purchases of items in the US, and had the data processed by CardSystems around Christmas.

“This was an issue that was discovered by our people around Christmas,” a National Australia Bank spokesman told the Australian Financial Review.

The NAB spokesman said only a few hundred of its 1.5 million credit cards had been involved and that they had been cancelled months ago.

The Commonwealth Bank revealed about 1,000 of its customers had been issued with replacement cards, while the ANZ replaced around 400 and Westpac’s victims also numbered in the hundreds.

MasterCard’s vice president of securities and risk, Tim Morris, defended the delay in publicising the scam saying it had taken time for the company to complete a detailed forensic investigation.

The latest account details given to Australian banks by MasterCard will be used to make sure no affected customers have been missed by previous checks.

Customers have been urged to contact their financial institution if they believe unauthorised transactions have been made using their accounts.