The public have been warned by police not to use Santander cash machines in Lancashire over fears they have been "compromised".
The warning follows reports of suspicious devices on the bank's machines across the county last week.
Officers are concerned criminals have targeted the machines in a bid to steal card details and cash, and urged those who have lost money to contact Santander.
Lancashire Police tweeted: "Security at Santander ATMs in Lancs has been compromised. Advice is not to use them. If you have lost money please contact the bank and 101."
A spokesman for the force said it is feared the issue could be more widespread.
He said: "We are advising the public to be vigilant, in particular of Santander machines, but of any cash machines.
"Report anything suspicious, have a visual check of the cashpoint and if in doubt leave it an go somewhere else."
"It's spread across the whole of Lancashire so it's highly likely other forces may have had reports. We do not know how many are affected."
The force also issued advice to bank customers, including not to use a cash machine if it appears to have been tampered with and shielding the keypad when entering the PIN number.
Cheshire Police have also issued a warning to avoid Santander machines in Wilmslow, near Manchester.
The force tweeted: "Cheshire Police have received reports of issues with Santander ATM's in Wilmslow. Please do not use the machines and call your bank and 101."