Gardaí are investigating after hundreds of Bank of Ireland accounts were skimmed at the weekend.
Thousands of euro were stolen after two branches in Graiguenamanagh, Co Kilkenny and in Borris, Co Carlow were hit.
It is understood fraudsters downloaded current account information by putting a small camera beside an ATM and an electronic device over the card slot.
Bank of Ireland says any affected customers will be reimbursed in the coming days.
Una Dillon from the Irish Payment Services Organisation says you must cover the key-pad when entering your PIN.
"It sounds like a simple thing but regardless of the amount of technology that the use and the money that these criminals have put into the equipment - if they can't see your PIN with the camera that is looking down at the PIN pad, they just really can't use your card's details," she said.
"So it's a simple thing.
"Don't worry about the people behind you, just cover your hand with your free hand when you are putting in the PIN."