Shoppers at Tescos in Springhill Retail Park in Bangor have been advised to check their bank accounts after a skimming device was uncovered at the ATM machine.
A couple who were about to use the machine alerted police to their suspicions and further scams were prevented.
However, it is unclear how long the skimming device had been inside the ATM.
A PSNI spokesperson said: "Thanks to an eagle-eyed members of the public, an ATM skimming scam has been foiled.
"This unassuming little device will steal your card details and fraudulent purchases will follow.
"This device was taken from the right side ATM at Tesco's Springhill and we would urge anyone who has used this machine in the last few days to check with their bank for any suspicious activity on their account.
"If you have seen any suspicious activity at this machine over the past number of days please contact police on 101 quoting serial number 1232 of 09/06/2019.
"If anything looks suspicious on an ATM do not use it. Report it to police on 101 and inform the relevant bank.
"We would like to extend a big thanks to the couple that reported this.
"They have saved a lot of people the grief of being scammed and have deprived organised criminals of a big payday."
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