NXP sues Mifare crackers
"We are aware that the Dutch researchers have reverse engineered the algorithm and we are taking this issue very seriously," said an NXP spokesperson at the time of the researchers' first announcement, speaking to the Times. "We've informed all of our system integrators and advised them to closely assess their systems. We're talking to the guys at Radboud University and have identified various counter-measures," continued the statement.
NXP also issued two application notes covering end-to-end system security risk considerations for implementing contactless cards. One is for contactless cards in general, while the other is specific for the use of Mifare Classic. These documents provide recommendations for implementing an appropriate level of security in systems using contactless cards.
At the same time, Transports for London (TfL), the British government agency in charge of mass transit in London area, issued a statement saying the security of Oyster, the local Mifare implementation, was not threatened. TfL says it is able to spot cloned cards immediately.