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The payment infrastructure went down for over five hours on Saturday morning, forcing drivers to allow people free entry to tube trains and buses.

The disruption was so severe because of the high level of reliance on the RFID card system. Over 17 million have been issued since their launch in 2003, and they now account for over 80% of journeys on the network.

However, some drivers unaware of the problem continued to allow users to swipe their cards during the downtime, potentially corrupting thousands of people's cards.

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number of cards used... may not be working as a result of yesterday's technical problem. Customers who topped up their cards at Oyster Ticket Stops during the day may also have been affected," says a statement from TfL yesterday, which advises that replacement cards are available for those affected from London Underground stations.

Last month it emerged that researchers from Radboud University in Holland had hacked the Oyster card system to gain a day's free travel on the network.

The group announced that it would be publishing details of the vulnerability at a security conference in October, but have now been sued by the makers of the chip to prevent this.

Yesterday the blog BoingBoing reported that the paper had nonetheless been posted on to Wikileaks, but the post today links only to a blank article on the site.