Slashdot

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.