The five-strong gang, who were all jailed this week, tampered with Chip and PIN devices in forecourts across five counties in order to copy data from customers' credit and debit cards.
Southwark Crown Court heard how gang members inserted Bluetooth-enabled devices into machines without the retailers' knowledge.
Cloned cards were then created and used across the globe. "Typically, retailers would have no idea that this kind of fraud was being conducted in their stores until it was too late," a spokesman for the UK Payments Administration told C-Store.
"These criminals have a lot of front and they manage to tamper with the devices by posing as engineers, planting fraudulent employees in the stores, or using classic distraction techniques," he added.
Retailers should regularly inspect equipment for signs of tampering, vet all new staff, and ensure that PIN pads are never left unattended.
The Chip and PIN scammers employ a variety of tactics, including:
l Placing illegal data-capturing devices in terminals by posing as bogus service engineers
l Stealing terminals and doctoring them prior to re-installing them in stores
l Stealing redundant equipment to capture any stored data
l Becoming an employee at the store or coercing existing staff into helping them access terminals
l Installing pinhole cameras or skim cards using handheld card readers
l Exploiting third-party suppliers