Opportunistic data thieves masquerading as bank technicians — have fooled shop owners into giving them access to credit card terminals and managed to download the details of over 20,000 credit and debit cards, it emerged this morning.

The Irish Payment Services Organisation has warned that individuals pretending to be from Irish banks convinced shop owners they were carrying out maintenance on behalf of banks.

This enabled them to plug in wireless devices that pushed the data to the internet and allowed the card numbers to be used overseas.

The scam has forced banks to restrict cash withdrawals to €100 a day for card holders travelling outside the country.

It is understood the scam was only uncovered by gardaí in the past 48 hours and they have retrieved CCTV footage of the gang in action.  Banks worked hard on the issue over the weekend and have either blocked or restricted access on cards affected. 

Until now criminals have focused mainly on putting devices on ATM machines to skim card data from consumers. However, this suggests a sinister, but startling overconfidence on the part of data thieves, who believe they can fool shop staff used to technicians working on the machines.

Retailers are being urged to check the identity of anyone claiming to be working on behalf of banks going forward.