Hundreds of Chip and Pin terminals in shops and supermarkets across Europe are believed to contain rogue chips that can transmit customers' card details.
US national counter-intelligence executive Joel Brenner told newspapers last weekend that international crime gangs could have tampered with Chip and Pin terminals during the manufacturing process in China.
It is believed an extra chip fixed to the back of the motherboard during manufacturing could have been responsible for millions of pounds being taken from European customers' accounts.
Customer card details, along with Pins, are said to have been copied over the last nine months and transmitted via mobile phone networks to fraudsters in Pakistan.
There are fears that money generated could have found its way to terrorists.
Asda and Sainsbury's are among the supermarket chains said to have been targeted by the fraudsters.
Brenner said "previously only a nation state's intelligence service would have been capable of pulling off this type of operation".
In 2006, police uncovered tampered Chip and Pin terminals in petrol stations.