Strike Force Wigg is investigating the use of skimming devices which steal card data to withdraw funds from accounts.

Fraud squad commander Detective Superintendent Col Dyson said that up to 50 members of an international crime syndicate had arrived in Australia to carry out the scam.

He said six had been arrested and that the $50million stolen had gone from 100-plus accounts in NSW in the past 12 months.

Mr Dyson said Eftpos terminals had been stolen, modified to copy information from magnetic strips on debit and credit cards, and put back into a different shop, including busy fast-food outlets, convenience stores and clothing retailers where

the thieves made further purchases using fake

cards.

``Some of those we've charged already have in fact been charged with armed robbery and the subject of those armed robbery offences are the Eftpos terminals,'' he said.

The unauthorised withdrawals are usually up to $1000 and show on bank accounts as occurring overseas.

Deborah and Greg Petrin, of Kellyville, have been reimbursed $2000 stolen last week from their NAB account and received new cards.

``But I don't know if we'll be using them because we don't want this to happen again,'' Mrs Petrin said. ``We're using cash and have transferred money to our credit card, which has to be signed.

``We'll continue to be wary until we get confirmation about the local places where it is happening.''

Mrs Petrin said more money might have been taken if she had not regularly checked her account balance and queried transactions.

Liam Pender reports: Banks will reimburse genuine victims of fraud. The Commonwealth Bank has sent text messages to customers whose accounts they believe may have been illegally accessed or who have used an ATM that may have been compromised.

A spokesman said the customers were asked to change their PIN. ``If they do not we automatically reduce their withdrawal limit,'' he said. ``If a customer has been genuinely skimmed we will refund the money.''

A Westpac spokeswoman said it blocks cards that it fears have have been skimmed and issues new cards within two to three working days.

``While a card is being reissued customers can still access their accounts via internet banking and can also withdraw cash at any branch,'' she said.