You've set your Facebook account to "friends only", your Tweets are protected and you wouldn't dream of setting a virtual foot near location-sharing services like Foursquare - in other words, you can feel pretty safe online, right? Wrong. We all unwittingly leak vital information through friends. "You can actually infer a lot of things about people, even though they are pretty careful about how they manage their online behaviour," says Adam Sadilek of the University of Rochester in New York. He has developed a system for predicting a Twitter user's location by looking at where their friends are. The tool can correctly place a user within a 100-metre radius with up to 85 per cent accuracy.
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