Amidst the ongoing debate over the value of privacy online, one thing is quickly becoming clear: It's very easy to identify people even when names and personal details are stripped from their data.
A team of computer science researchers from Columbia University and Google have just proved that geotagged posts from only two social media apps are enough to link accounts held by the same person.
It turns out that our real-world movements are so distinctive from person to person that people can be identified from just a handful of datapoints. Previous research has shown that individual shoppers can be picked out of a dataset of millions of credit card shoppers with as little as four purchases.
Probability
This new study compared geotagged Twitter posts with posts on Instagram and Foursquare to try and link accounts owned by the same person. To do that, the researchers developed an algorithm that calculated the probability that one person posting at one time and place could be the same person posting in a different app at another time and place.
Not only does it identify people, it can also reveal information about them like their age, gender, ethnicity, household income and whether or not they have children.
One of the study co-authors, Chris Riederer, previously built an online tool that guesses various things about you if you hook up Foursquare, Instagram and Twitter accounts here, though it doesn't really work outside of the United States.
Change Your Behaviour
"People are now sharing their location on a growing number of apps, often without realizing it," said Riederer. "Companies no longer have to be very sophisticated to access this data and use it for their own purposes."
"Many people choose not to identify themselves online," said another of the study co-author, Augustin Chaintreau. "If I now tell you that your location data makes you recognizable across all of your accounts, how does that change your behavior? This is a question we now have to answer."
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