Details of a computer hack which allowed researchers to clone identity cards that are used by million of people to access buildings and travel on public transport are to be published.

The company which makes the Mifare smartcard, which is used to gain access to thousands of British schools as well to ride on the London Underground and buses, had sought to prevent Dutch researchers from publishing details of the hack.

But a court in Holland has overturned an injunction that would have prevented the publication of the research, paving the way for academics from Radboud University to explain how they were able to ride the Tube free for a day with a cloned Oyster card - and sneak into Dutch government buildings.

After learning of the breach in April, the Dutch government posted armed guards outside all its buildings, and postponed the introduction of a new €1 billion transport payment system similar to the Oyster card until the security issues had been addressed.

Oyster card cloning with a laptop

Mifare smartcard is hacked into by Dutch university scientists, highlighting security flaw on identity and swipe cards

• ID cards are the ultimate identity theft

• We’ve sold our secrets for a walletful of plastic

Professor Bart Jacobs, who led the research team, said he would hold off publishing his findings until the Dutch Government and NXP, which makes the technology used in Mifare cards, had had a chance to make their systems more resilient.

But NXP sought an injunction to ensure the details of the hack would never be made public. A court in Arnhem has now overturned the injunction, citing freedom of expression laws. "(The) damage to NXP is not the result of the publication of the article, but of the production and sale of a chip that appears to have shortcomings," the court said.

Radboud University welcomed the ruling, saying that "in a democratic society it is of great importance that the results of scientific research can be published".

A spokesman for NXP, which was formerly a division of Philips, the electronics manufacturer, said: "We don't mind them publishing the effects of what they have discovered to inform society. I think this is absolutely fine. But disclosing things in detail including the algorithm ... is not going to benefit society, it will create damage to society."

Transport for London said it remained confident that the Oyster card system, used by millions of people on London's Tube and bus network, was secure, but added that it was "constantly reviewing" its security procedures.

The Dutch Interior Ministry said at the time the hack was made public that it was replacing 120,000 cards used by civil servants to access Government buildings. About ten million Mifare smartcards are sold in Britain each year, and are used to access public buildings as well as in contactless payment systems.

Explore Tech & Web

• Personal Tech

• The Web

• Gadgets & Gaming