Police are urging bank customers to check cash machines before using them, after a gang were put behind bars for a hi-tech card scam worth up to £200,000.
The gang replaced the fascia of the cash machines
On Thursday, three illegal immigrants and an asylum seeker admitted carrying out the electronic fraud in Cardiff.
The gang put false fronts on the cash machines, and installed cameras to film people tapping in their pin numbers.
Three were given four-year jail terms and the fourth was sent to a young offenders' institute for four years.
Rulan Ashan, 20, from Chechnya, Lucian Carabgeac, 32, from Romania, Ivan Grosu, 23, from Moldova and Vornicu Florin, 26, also from Romania, were sentenced at Cardiff Crown Court.
After the trial, Detective Constable Paul Giess said police were repeatedly finding that eastern Europeans were behind this kind of card fraud.
"From our investigations, it appears that all recent incidents over the last 18 months have involved eastern European gangs," he said.
"We were surprised at how sophisticated this operation was. I've never dealt with anything like this before."
Martin Lewis, from Cardwatch, which helps the banking industry tackle fraud, said there were "lots of things" that people could do to tackle the problem.
"First and foremost, please put your safety first, and be vigilant at all times when using a cash machine," he said.
The four men all admitted conspiracy to steal
"When you are using one, please shield your pin with your free hand - that way a camera can't see your pin number and nor can anyone looking over your shoulder."
"At industry level, we have chip and pin which will eradicate skimming totally, banks have their own initiatives in place and clearly the police have a role to play as well."
But he added that banks would repay funds if people are caught out as innocent victims of this sort of crime.
Aled Williams, from NatWest bank, said machines had since been enhanced to make this type of crime more difficult.
"We have introduced the chip-and-pin system as well to make copying and cloning of cards more difficult," he said.
The London-based gang in Cardiff were caught after Ramona Pritchard, the receptionist at the Cathedral Hotel, reported that they were acting suspiciously.
Delivering the sentences, Judge Christopher Llewellyn-Jones said Ms Pritchard's part should be recognised.
"I think the banks ought to reward that lady," he said. "She's probably saved them a considerable amount of money."