Details from chip-and-pin cards could be stolen while shoppers make purchases, scientists discovered in an investigation for BBC One's Watchdog.
Cambridge University researchers said details could be hijacked if a card is put into a doctored payment machine.
Details can then be sent wirelessly to accomplices and purchases made using a fake card with those account details.
A spokesman for UK payments association Apacs said there was no evidence the method had been used in the UK.
Viewers of Tuesday night's Watchdog programme can watch the Cambridge University team intercepting cardholder's details during a transaction in a book shop before sending them wirelessly to an accomplice.
A fake card was made up with the account details and further purchases were made.
The scam can only be carried out if unscrupulous staff insert cards into tampered machines before alerting accomplices outside the store.
Watchdog producer Alan Holland said the exercise showed the chip-and-pin system was "not infallible".
"These academics are clever but there are thieves out there who are going to be equally clever but more driven," he added.
"It is not particularly expensive to do and it hasn't been that complex as an electronic process."
Apacs' Sandra Quinn said such fraud would be difficult because it would need an in-store accomplice and an external accomplice to work at the same time.
"I think we should be more concerned about other types of fraud - there is no evidence that this is about to happen," she said.
"It is on the list of potential threats, as lots of other things are."
Watchdog will be screened on BBC One on Tuesday at 1900 GMT.