95% of the mobile users can be uniquely identified from location data
It isn’t hard to think of a dozen films where at some point in the story a tracking device is placed on a person, car or ship so that someone can keep tabs on them. Well, that might be fiction but the truth is that millions of people willingly carry around tracking devices every day – their mobile phone. New research published in Nature has shown that by cross referencing location data with other freely available data sources it is possible to track 95% of mobile phone users using what is meant to be anonymous location data!
The research is full of some heavy statistical analysis of around 1.5 million mobile phone users who had the location of their nearest cell tower recorded every time the they interacted with the phone network (by making a call, receiving an SMS and so on). The data was recorded in 2006 and later analysed. The researchers found that if the phone interacted with the carrier’s network once an hour it is possible to uniquely identify 95% of the individuals.
The idea is basically this, if I am in location A and receive a call then the anonymous data shows approximately where the call was received and a dot is placed on the map. If I then move to location B and receive another call, that call appears as a new dot on the map. But the dot from location A has now gone. By tracking all the other dots and by a process of elimination it is possible to work out that the phone used to receive the call at location A is the same phone now in location B. If either location is a known address like my house or my office it is quite easy to use other data, like a voters list, to start linking the phone data with an individual.
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