Internet banking customers were warned tonight about a fraudulent scheme to steal their credit card details.
Allied Irish Bank said two of its clients had complained about mysterious pop-up screens which requested credit card numbers, expiry dates and PIN numbers.
The screens appeared yesterday after the clients had logged into the credit card section of their accounts on AIB's 24 hour banking website.
AIB spokesman Mr Trevor McEvoy warned customers the screen was a fraudulent attempt to obtain personal details.
"We believe it came from a software virus that was installed in the customer's PC and is likely to have come in by email," he said.
The bank also learnt of a third customer who encountered the fake screen on an online shopping website.
The practice of using spoof e-mails and fraudulent websites to extract credit card details from bank customers is known as 'phishing'.
The details can then be used to make a copy of the credit card, which enables the criminal (who also has the PIN number) to empty the customer's bank account.
But the Irish Payment Services Organisation (IPSO) said the infiltration of banking websites with fake screens was a worrying development.
"This is a totally new type of phishing," said spokeswoman Ms Una Dillon.
She warned customers not to divulge credit card PIN numbers, which would never be requested by a genuine bank.
"This is carried out by people associated with Eastern European gangs, connected in some cases to the Russian Mafia. They don't have any morals and they're very focused in what they do."
AIB is hoping to examine the computers of the two clients to discover which email delivered the virus.
AIB Internet customers can contact a helpline at 1890 242001.