Forget about hacking your Apple iPhone, Dutch researchers have worked out a way to hack Transport for London’s Oyster Card.

Details of how to copy the Oyster cards - that are used by millions on London's transport network - will be published in October, according to the BBC.

NXP, the makers of the travel smartcards, had won an injunction suppressing the information, but a Dutch court has now overturned this.

The security weaknesses in the Oyster card were discovered by Prof Bart Jacobs and colleagues from Radboud University, Nijmegen in March 2008.

According to the BBC report, the weaknesses centre around the Mifare Classic chip that sits at the heart of the contactless card system.

As well as being used on the 6m million Oyster cards in regular use, the Mifare chip is also used in Hong Kong's travel network, and is the basis of the Dutch Rijkspas smartcard.

Oyster is London's ticketing and revenue system. The Oyster Card can store up to £90 of cash that can be used to pay as you go, plus Travelcard or Bus Pass accounts.

Governments, also use the Mifare technology as a secure entry system for buildings.

NXP spokesman Christophe Duverne told Reuters that it would take months or years for some users of the chip to adapt their systems to defend against the attack.

"We don't mind them publishing the effects of what they have discovered to inform society, I think this is absolutely fine," he said. "But disclosing things in detail including the algorithm ... is not going to benefit society, it will create damage to society."