How Facebook can have your data even if you’re not on Facebook

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One of the creepiest things brought to light during Mark Zuckerberg’s testimony on Capitol Hill this week was how Facebook can amass data to construct what are being referred to as “shadow profiles” of you, even if you’ve never opted in or joined the world’s largest social network.

Facebook’s CEO told Congressman Ben Lujan, D-N.M., that he was unfamiliar with shadow profiles as a term but acknowledged that “in general,” Facebook collects information on people who have not signed up for the service, which it does for “security purposes.”

But privacy advocates worry about what happens to that data when it is in Facebook’s control and not yours, or for that matter slips out of the company’s grasp. Facebook may have privacy tools and policies that members of the Facebook community can opt in or out of (assuming they can understand them), but it’s a whole different deal if you’re not on a social network that is getting the skinny on you anyway.

What do they know?

One of the main ways the social network can gather details on someone who hasn’t signed up occurs when someone you know who is on Facebook shares his or her phone contact list with the service, which they’re encouraged to do so that they can more easily find their friends. At the very least Facebook may discover your address, phone number and email this way, and, obviously also knows that you know the friend who revealed the contact list.

Your friends may also tag you in photos and, wittingly or not, spill the beans on other details you might otherwise wish to keep private.

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