According to security blogger Brian Krebs, gang members managed to take around $9 million from cash machines in more than a dozen countries in a matter of hours on Christmas Eve. This was followed up just before New Year's Eve by an attack on a card network in India which saw the thieves make off with around $2 million.

In an alert - published by Krebs - to issuers, processors and ATM acquirers, sent out shortly after the second attack, Visa warns that further attempts are expected, urging increased vigilance.

The attacks, Visa explains come from hackers gaining access to issuer authorisation systems and card parameter information. Continues the alert: "Once inside, the hackers manipulate daily withdrawal amount limits, card balances and other card parameters to facilitate massive fraud on individual cards."

Meanwhile, US authorities have charged 18 people with creating thousands of fake identities to obtain credit cards and steal more than $200 million.

Yesterday morning, hundreds of FBI and the US Postal Inspection Service officers swooped and arrested 13 defendants and searched 13 locations in New Jersey, New York, Pennsylvania, and Connecticut in a bid to take down what authorities call a "sprawling criminal enterprise".

The defendants charged in a complaint unsealed yesterday allegedly fabricated identities to obtain credits cards and doctored credit reports to pump up the spending and borrowing power associated with the cards.

They would then borrow or spend as much as they could and not repay the debts, looting businesses and financial institutions of more than $200 million in confirmed losses.

All the defendants are charged with one count of bank fraud, which carries a maximum potential penalty of 30 years in prison and a fine of $1 million.

US Attorney Paul Fishman says: "Through their greed and their arrogance, the individuals arrested today and their conspirators allegedly harmed not only the credit card issuers, but everyone who deals with increased interest rates and fees because of the money sucked out of the system by criminals acting in fraud rings like this one."