Your Personal Info Might Be on Facebook — Even if You Aren’t

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Think staying off social-networking sites will help you preserve your privacy? Think again. In a new study, German researchers found that they could find substantial amounts of personal information about people who weren’t Facebook members just by seeing what their friends who were on Facebook posted about them.

The researchers were able to figure out with a high degree of accuracy whether or not people who were non-Facebook members knew each other. “We show that the seemingly innocuous combination of knowledge of confirmed contacts between members on the one hand and their e-mail contacts to non-members on the other hand provides enough information to deduce a substantial proportion of relationships between non-members,” they wrote.

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The effect is more pronounced when Facebook users open up their e-mail-contact lists to the platform, since that list probably includes other Facebook users as well as those who aren’t members. The researchers predict that the number of people on Facebook who give the site access to their e-mail contacts will only increase in the future.

Ironically, this means that people who are obsessed with their privacy could actually benefit from joining social-networking sites. As a member, you can keep track of who’s tagging you in photos, for example, and remove the tag if you want. If you’re not a member, you have no way of knowing what information your friends are disseminating about you.

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Although the experiment focused just on finding real-life friend connections between nonmembers, researchers said their study’s “astonishing” conclusion has broader implications. For instance, they pointed to a 2009 study that shows it’s really simple to figure out undisclosed details about a person, such as sexual orientation, based on related information disclosed by their friends. “Ultimately, it evokes the question of the ownership and exploitation of relational data in the information age,” they wrote.

Social networks in general, and Facebook in particular, have a vast trove of data encompassing everything from users’ entertainment preferences to locations. With the help of some sophisticated statistical models, other people or companies can find out and predict a lot more about you than you might imagine, even if your profile is private — or even nonexistent.

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