Stalkers Exploit Cellphone GPS

Phone companies know where their customers' cellphones are, often within a radius of less than 100 feet. That tracking technology has rescued lost drivers, helped authorities find kidnap victims and let parents keep tabs on their kids. But the technology isn't always used the way the phone company intends.

Global-positioning systems, called GPS, and other technologies used by phone companies have unexpectedly made it easier for abusers to track their victims. A U.S. Justice Department report last year estimated that more than 25,000 adults in the U.S. are victims of GPS stalking annually, including by cellphone. In the online world, consumers who surf the Internet unintentionally surrender all kinds of personal information to marketing firms that use invisible tracking technology to monitor online activity. A Wall Street Journal investigation of the 50 most-popular U.S. websites found that most are placing intrusive tracking technologies on the computers of visitors -- in some cases, more than 100 tracking tools at a time.