More than 30 people have lost money in the last month in a complex cash machine scam at banks in mid and west Wales.
People are being urged to take care at cash points
Dyfed-Powys Police say over £3,000 has been taken from people's bank accounts using a device which is often known as the Lebanese loop.
The con-trick has been used at banks and building societies in Aberystwyth, Newtown, Llandeilo, Ammanford and Carmarthen.
Detectives are now urging card holders to take extra care when using cash machines.
As part of the scam a device is placed in the cash machine so that when people go to use it, it swallows their card.
That person is then approached by a passer-by who suggests they try re-typing their bank pin number in to try and get it back.
The passer-by watches and memorises the number, later retrieving the device and the card.
Last year four people were arrested and convicted after being caught operating the scam in Llanelli.
But Inspector Alan Lewis said: "This is still happening and there have been over 30 incidents over the last month.
"Offences generally occur at night or on Saturdays and Sundays so that the victim cannot make enquires with the bank until the following Monday."
He urged anyone who sees anything suspicious to contact police straight way.
Inspector Lewis said anyone using cash machines should take certain precautions.
"Before entering your card run a finger along the card slot to feel if there is a loop in place," he said.
"ATMs will inform you on the screen if they retain your card.
"If the screen does not inform you of this fact you should be alerted to a possible con trick.
"Do not re-enter your PIN number in view of any passer-by."