Identifying People from Mobile Phone Location Data

Turns out that it's pretty easy:

Researchers at the Massachusetts Institute of Technology (MIT) and the Catholic University of Louvain studied 15 months' worth of anonymised mobile phone records for 1.5 million individuals.

They found from the "mobility traces" - the evident paths of each mobile phone - that only four locations and times were enough to identify a particular user.

"In the 1930s, it was shown that you need 12 points to uniquely identify and characterise a fingerprint," said the study's lead author Yves-Alexandre de Montjoye of MIT.

"What we did here is the exact same thing but with mobility traces. The way we move and the behaviour is so unique that four points are enough to identify 95% of people," he told BBC News.

Here's the study.

EFF maintains a good page on the issues surrounding location privacy.