"Currently the security services can demand the Oyster records of specific individuals under investigation to establish where they have been [3,000 requests for passenger journey data in 2006] but cannot trawl the whole database. But supporters of calls for more sharing of data argue that apparently trivial snippets — like the journeys an individual makes around the capital — could become important pieces of the jigsaw when fitted into a pattern of other publicly held information on an individual's movements, habits, education and other personal details. That could lead, they argue, to the unmasking of otherwise undetected suspects.
Boiled Frog from a Nation of Suspects (582566) writes "The Oyster card, an RFID single-swipe card (recently cracked) was introduced to London's public transport users purportedly to make their lives easier. Now British Intelligence services want some of the benefits by trawling through the travel data amassed by the card to spy on the 17 million Britons who use it.