March 27, 2013
Researchers Show They Can Track You By Your Cellphone Data
Lee Rannals for redOrbit.com — Your Universe Online
The new formula developed by the team shows how weak the privacy of cellphone data really is, but could pave the way for a better policy discussion.
The team analyzed data on 1.5 million cellphone users in a small European country over a span of 15 months and found just four points of reference was enough to identify 95 percent of them. In other words, all you need to extract the complete location information for a single person from "anonymized" data is to place them within a couple hundred yards of a cellphone transmitter over the course of an hour, four times in a year.
Their formula shows the probability of identifying someone goes down if the resolution of the measurements decreases, but less than you would think. The formula would still de-anonymize you even if the reported time of measurement was within a 15-hour span, or location was imprecise like somewhere amid 15 adjacent cell towers.
“There´s a concern with this data, to what extent can we preserve anonymity,” says Luis Bettencourt, a professor at the Santa Fe Institute who studies social systems. “What they are showing here, quite clearly, is that it´s very hard to preserve anonymity.”
He points out it is interesting from a scientists' perspective, to understand how people use urban space, showing what kind of social systems cities are in.
The team believes similar relationships could exist for other types of data.
“I would not be surprised if a similar result – maybe requiring more points – would, for example, extend to web browsing,” said CÃ©sar Hidalgo, an assistant professor of media arts and science. “The space of potential combinations is really large. When a person is, in some sense, being expressed in a space in which the total number of combinations is huge, the probability that two people would have the same exact trajectory – whether it´s walking or browsing – is almost nil.”
The researchers hope their formula will provide a way for researchers and policy analysts to reason more rigorously about the privacy safeguards that need to be put in place.
“Both CÃ©sar and I deeply believe that we all have a lot to gain from this data being used,” says Yves-Alexandre de Montjoye, a graduate student in the research group of Toshiba Professor of Media Arts and Science Sandy Pentland. “This formula is something that could be useful to help the debate and decide, OK, how do we balance things out, and how do we make it a fair deal for everyone to use this data?”
There are a few smartphone apps available for those who are really worried about maintaining privacy. Computer scientists from SaarbrÃ¼cken developed the app "SRT AppGuard" to keep smartphone applications from stealing personal information. Although this app ensures your information stays away from third parties while online, it doesn't safeguard you from everything, including those lurking around cellphone towers for incoming data.