Police have warned that the sophisticated electronic scam involving cash-machines is spreading across Wales.
The cloning device is made to look like part of an ATM
South Wales Police were the first force to find cloning devices attached to cash machines to clone cards, but eight cases have since been reported in Llanelli, west Wales.
Detectives from Dyfed-Powys Police said customers had found large amounts of money stolen from their accounts, and they have warned anyone using a machine to check to see whether they have had any unauthorised withdrawals.
It is feared that the machines have been used to gain the details of hundreds of accounts in recent weeks.
Police are warning people to check their statements after the discovery of the devices over the weekend at several banks in locations including Queen Street and St Mary Street in Cardiff, Penarth and Port Talbot.
In the past week, 15 people have told South Wales Police about missing funds from their accounts as a result of cloning. One one man had £3,500 stolen from his account.
"This is a very sophisticated way of accessing account details and there is a great deal of concern about it," said Detective Constable Terry Stevens.
"The criminals are able to copy the details of the cash cards from the magnetic strips and programme them onto the strip of a donor card which can be used to withdraw money.
"This is organised crime by gangs which we suspect originate from London, possibly Eastern European gangs."
The device, which is attached to the card slot of the machine, works by recording the details on the magnetic stripe of the card as it passes through.
The personal identification number (PIN) is then accessed either by someone watching as the ATM is being used or by secret camera equipment.
The criminal can then create a copy of the card by removing the device and using a lap top computer to download the information on to any card with a magnetic strip - a store card for example.
It looks exactly like the ATM machines and money is dispensed to customers in the usual way.
As well as checking statements, Mr Stevens urged people to be vigilant when using cash machines.
"Be wary if the card slot on the ATM seems unsecured or protrudes unusually, or if there is anything unusual attached to the ATM that wasn't there before like a small bin," he said.
"And alert the bank to anything which looks suspicious."
Anyone who believes they may have been affected should report any suspicious withdrawals to the police and their bank immediately who will be able to check if their cash card had been cloned.
For Cardiff solicitor Simon Mumford, the story brought back memories. He was on holiday last year in South Africa and had his credit card cloned.
Around £2,000 went missing from his account, with transactions taking place in Egypt - a place he had never been.