Cell Phone Users Secretly Tracked

June 4, 2008 -- Researchers secretly tracked the locations of 100,000 people outside the United States through their cell phone use and concluded that most people rarely stray more than a few miles from home.

The first-of-its-kind study by Northeastern University raises privacy and ethical questions for its monitoring methods, which would be illegal in the United States.

It also yielded somewhat surprising results that reveal how little people move around in their daily lives. Nearly three-quarters of those studied mainly stayed within a 20-mile-wide circle for half a year.

The scientists would not disclose where the study was done, only describing the location as an industrialized nation.

Researchers used cell phone towers to track individuals' locations whenever they made or received phone calls and text messages over six months. In a second set of records, researchers took another 206 cell phones that had tracking devices in them and got records for their locations every two hours over a week's time period.

The study was based on cell phone records from a private company, whose name also was not disclosed.

Study co-author Cesar Hidalgo, a physics researcher at Northeastern, said he and his colleagues didn't know the individual phone numbers because they were disguised into "ugly" 26-digit-and-letter codes.

That type of nonconsensual tracking would be illegal in the United States, according to Rob Kenny, a spokesman for the Federal Communications Commission. Consensual tracking, however, is legal and even marketed as a special feature by some U.S. cell phone providers.

The study, published Thursday in the journal Nature, opens up the field of human-tracking for science and calls attention to what experts said is an emerging issue of locational privacy.