An oft-repeated refrain among the privacy conscious is that a mobile phone is really a tracking device that lets you make calls. But a major new study suggests the digital trail left by a mobile phone can identify more than mere movements - it can be used as a "fingerprint" to identify people with a striking degree of accuracy.
In a report published this week, a team including researchers from MIT and Harvard revealed that anonymised mobile phone location data demonstrate patterns of behaviour that could be used to identify a person. They were able to "uniquely identify 95 per cent of the individuals" so long as they had hourly updates showing mobile phone location and could measure it against four distinct "spatio-temporal points" on a map. The finding was significant. It illustrates "fundamental constraints to an individual's privacy," according to the researchers.
The data on the 1.5 million people were obtained from an unnamed mobile phone operator in a "small European country" and covered a 15-month period. Location data over time, for instance, could be used to help pinpoint where users worked, where they shopped, where they went to relax on the weekends, where and when they left the country and from which airport they departed, and more. Of course, the researchers didn't identify any users by name in their study - but the point is that it wouldn't be difficult to do.
"Given the amount of information that can be inferred from mobility data, as well as the potentially large number of simply anonymised mobility datasets available, this is a growing concern," the report noted. "The information that can be inferred from [the data] highlights the importance of understanding the privacy bounds of human mobility."
It's fairly common for app providers to gather location data on users. The researchers pointed out that an estimated one-third of the 25 billion apps downloaded from the Apple App Store access a user's geographic location, and about 50 per cent of all iOS and Android traffic is available to ad networks. Mobile phone location data are widely used by law enforcement, too, with authorities in some cases using "tower dumps" to obtain information showing the movements of all individuals in a target area at a specific time. The US Justice Department has recently claimed that users have no reasonable expectation of privacy over their location data - though this latest study may go some way to discrediting that argument. It may also fuel support for a proposal, that would force app providers to ask users for consent to record their movements.