The skimming devices are capable of copying card details, while a video camera records people entering their personal identification numbers.

The skimming devices are capable of copying card details, while a video camera records people entering their personal identification numbers. Photo: Michael Clayton-Jones

ATM scammers have become so sophisticated, it may no longer be good enough to use your hand to hide your PIN, police warn.

Two foreign nationals - a Hungarian and a Romanian - were arrested last month after allegedly tampering with an ATM in Sydney's central business district. But police believe others are still out there fitting skimming devices to ATMs.

Police say two men - both of Eastern European appearance and aged in their 20s or 30s - are also wanted for questioning.

They say more than 40 ATMs in Sydney, including those in Mosman, Double Bay, Dural and Parramatta, have been targeted since January.

A gang with links to Eastern Europe is believed to be behind the rise in cases.

The commander of the fraud and cyber crime squad, Arthur Katsogiannis, said the criminal group was highly organised and sophisticated and had already bagged more than $100,000.

''This type of crime is the choice of criminals in the 21st century,'' he told reporters in Sydney on Monday. ''With the advent of technology advancing at an exponential rate, this will be more and more common.''

The skimming devices used by the group are capable of copying card details, while a tiny video camera records people entering their personal identification numbers. A copy of the card is then created, allowing the group to access the account holder's funds.

Detective Inspector Matt Craft said that while earlier cameras were only able to pick up footage from the top of the keypad, they were now finding more sophisticated cameras that could pick up different angles.

Detective Inspector Craft urged the public to be more vigilant when using ATMs by covering the keypad while typing in their PIN.

''Use your wallet, your purse, a newspaper or something else so it's covered virtually [all over] and not just the top,'' he said.

''That's the best way to combat this particular type of crime.''

AAP