Bits of you are all over the Internet. If you've signed into Google and searched, saved a file in your Dropbox folder, made a phone call using Skype, or just woken up in the morning and checked your email, you're leaving a trail of digital crumbs. People who have access to this information — companies powering your emails and Web searches, advertisers who are strategically directing ads at you — can build a picture of who you are, what you like, and what you will probably do next. Revelations about government counter-terrorism programs such as PRISM indicate that federal agents and other operatives may use this data, too.
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For example, when a group from MIT analyzed location data from cellphones of 1.5 million people in a single country over 15 months, the team could identify individuals simply by knowing where they were on four separate occasions.
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Advertisers already track our lives with astonishing accuracy going off very little information — Target has known when a woman was pregnant even before her family did. And just as advertisers are profiling you to make money, law enforcement and counter-terrorism operatives make use of these clues to hunt for suspects.
