Your Apps Know Where You Were Last Night, and They're Not Keeping It Secret

Dozens of companies use smartphone locations to help advertisers and even hedge funds. They say it's anonymous, but the data shows how personal it is. From a report: The millions of dots on the map trace highways, side streets and bike trails -- each one following the path of an anonymous cellphone user. One path tracks someone from a home outside Newark to a nearby Planned Parenthood, remaining there for more than an hour. Another represents a person who travels with the mayor of New York during the day and returns to Long Island at night. An app on the device gathered her location information, which was then sold without her knowledge. It recorded her whereabouts as often as every two seconds, according to a database of more than a million phones in the New York area that was reviewed by The New York Times.

At least 75 companies receive anonymous, precise location data from apps whose users enable location services to get local news and weather or other information, The Times found. Several of those businesses claim to track up to 200 million mobile devices in the United States -- about half those in use last year. The database reviewed by The Times -- a sample of information gathered in 2017 and held by one company -- reveals people's travels in startling detail, accurate to within a few yards and in some cases updated more than 14,000 times a day.

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