CASH machines in Llangollen have been targeted by 'skimmers' - criminals who tamper with the card slot in order to steal card details.
In the fortnight before Easter a number of Automatic Telling Machines (ATMs) - also known as the hole in the wall - were targeted.
Skimmers insert a device into the card slot that looks like a normal slot but is attached to a computer board. When a customer inserts their card everything seems to work normally but the device copies all the card data and can then be used to create fake cards to empty bank accounts or steal someone's identity.
Some devices hang on to the card and are taken away by the watching gang once a customer goes inside the bank to complain.
These devices come in many varieties. some are crude and home-made, others are difficult to spot unless customers are paying attention.
Some even come in the form of whole ATM fascias so the only way to tell is to check whether it looks stuck on.
NatWest first identified the problem in Llangollen on March 12.
On both the Saturday and the Sunday devices were discovered in its ATM. The bank reported it to the police.
It is believed that a skimmer may also have been placed in the machine on Sunday, March 20, although the bank says it knew nothing about the second incident.
Other banks in the town, Barclays and HSBC, have reported no problems in their machines.
Aled Williams, spokesman for NatWest, said: 'This type of fraud is an industry-wide issue which affects all UK banks.
'We are working closely with the police and the Association for Payment Clearing Services (APACS) to combat this crime.
'When we discovered the skimmers in Llangollen, we notified the police immediately but it is not isolated to a particular area or a particular bank and machine users should always take care
'Always shield your pin number from others, no matter who they are, never disclose it to anyone who claims to be from the bank or police, as neither would ever ask for it, and if you are concerned that something is wrong or suspicious about the cash machine you are using try to stay with it and your card.
'Ask someone else to go into the bank for you to alert a member of staff or phone the bank or police from the machine. If this is not possible contact your bank and the police as soon as possible.'