Police have issued a fresh warning about cash machine fraud after banking experts uncovered new information about the criminals' methods.

A total of 14 offences were originally identified in Hertfordshire during June, with reports that bank cards were retained by ATMs and cash was later withdrawn from accounts. 

It was originally thought devices placed over the car slots were being used to scan cards and transmit details and the PIN to fraudsters.

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But police say an investigation by banking experts suggests that the criminals watched the victim input the PIN and then retrieved the trapped card before using the card and PIN at another ATM.

Hertfordshire Constabulary recommends always shielding the input when entering your PIN into a cash point and looking carefully at the ATM for tampering before use.

Detective Sergeant Mark Fava from the force’s Serious Fraud and Cyber Unit said: “The best way to avoid this happening to you is to cancel or suspend your bank card if it is retained by an ATM."