Many marketers have made no secret of their desire to target ads to mobile users based on their location.
But a new study indicates that geo-location targeting -- even when theoretically “anonymous” -- raises significant
privacy concerns. For the study, researchers at MIT and the Catholic University of Louvain studied fifteen months' worth of "anonymized" data gleaned from 1.5 million people over a 15-month period.
From that trove of information, the researchers concluded that “human mobility traces are highly unique.”
The report states: “In a dataset where the location of an individual
is specified hourly, and with a spatial resolution equal to that given by the carrier’s antennas, four spatio-temporal points are enough to uniquely identify 95% of the individuals.”
Even when the researchers “coarsened” the data, they still found that people could be identified. “Hence,” the paper continues, “even coarse datasets provide little
anonymity.”
That conclusion doesn't mean that geo-location targeting is illegal, only that it's probably not anonymous in any meaningful sense. But any companies who say in privacy
policies that they collect anonymous geo-location data collection might need to rethink that language.
Overall, the report offers yet another piece of evidence that individuals can be
identified based on “anonymous” data -- a prospect that privacy experts like Paul Ohm have warned of for years.
To some extent, this has already happened. The most famous
example occurred in 2006, when AOL released three months worth of search queries for 650,000 users. The searches alone provided clues to some of those users' identities.
That's not the only
incident. Several years ago, two computer scientists at the University of Texas reported that it was possible to identify users by comparing reviews of obscure movies on Netflix with reviews on
Imdb.com that were published under screennames. Last year, a federal prosecutor was identified as an anonymous commenter at the Times-Picayune's NOLA.com, based on
the vocabulary he used in his posts.