Facebook users' frequent decisions to open troves of personal information to people they don't know well online is predicated on a comforting assumption: You can always "defriend" an offending party, walling him off once more from your FB profile.
Yet a new study by researchers at University College London indicates that things might not be that simple, and that a loophole in the social-networking site makes it a lot harder to ditch a persistent "Facebook stalker" than you might expect.
Computer scientists Yvo Desmedt and Shah Mahmood found that by deactivating a profile, a hypothetical Facebook stalker makes himself unavailable for defriending -- that is, being removed from the list of FB users with access to a given person's profile page.
However, Facebook encourages those people to reactive their accounts, incentivizing users by making available to them the same list of "friends" they had at the time of cancellation. So the stalker can simply sign up again to get access to a former friend's profile page.
Desmedt and Mahmood call this the "cloaked spy" phenomenon in their paper. The stalker can "cloak" himself by temporarily deactivating and then reactivating his account, making himself immune to defriending in the interim.
Who knows -- some of those folks you thought you had defriended might merely have cloaked themselves, and could be checking out photos of your dog right now.
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