Hertfordshire Constabulary told residents to be vigilant after several reports of thefts where bank cards were retained by the machines.
Victims later discovered cash had been withdrawn from their accounts, after the loss of their card.
What has been said?
Detective Sergeant Mark Fava, from Hertfordshire Constabulary’s Serious Fraud and Cyber Unit, said: “It appears that these thefts are being achieved by a discreet device being placed over the card slot of the machine, which scans the card details, transmits the data to the criminal and then blocks the card from being returned.
"The best way to avoid this happening to you is to cancel or suspend your bank card if it is retained by an ATM. If you have a banking app on your phone you may be able to freeze your card temporarily until you can establish what has happened. Alternatively, you may need to call your bank to cancel or suspend the card until it has been recovered.”
How to protect yourself against this type of scam?
If your card is retained by an ATM, call your bank and ask for it to be frozen immediately or cancelled.
This may also be an option via an app on your phone.
When withdrawing cash, take usual precautions such as shielding the keypad when typing in your PIN and always examine the machine before use.
If anything looks out of place, or there are parts that look added on, do not use it and report your suspicions to the bank.
If the machine fails to return your card or any cash you have withdrawn, you should contact the police on the non-emergency number, 101, and your bank to inform them.
The police force is urging Brits to take the following precautions when using cash machines:
1. Always look closely at the card insertion point of a cash machine before using it. If it looks like it may have been tampered with, do not use it.
2. If you realise the machine has been tampered with after you have inserted your card, call your bank while still standing at the cash machine if it is safe to do so.
3. Always shield your hand when entering your PIN into a cash point keypad.
4. If the machine retains your card or fails to dispense cash you have withdrawn, without a suitable explanation message on the screen, contact your bank immediately and then police on our non-emergency number 101.
A version of this article originally appeared on NationalWorld.com