American Civil Liberties Union

So, you’ve done it all right. You’ve meticulously chosen your Facebook privacy settings so that only your closest friends can see the most personal information about you. No one else has access. Or so you think.

Turns out, it’s more like your designated closest friends and anyone who advertises on Facebook. (And, P.S., anyone *can* advertise on Facebook. Doesn’t have to be a business.) Sure, advertisers aren’t given the exact identities of the individuals who are served their ads, but given the precise way that advertisers can choose their target audience — by some combination of location, age, interests, employer, etc. — anyone with a few cents to spend on an ad can undoubtedly unmask your most personal details if he/she wants to. In fact, Stanford Computer Science researcher Aleksandra Korolova has done just that. (Don’t worry — she targeted a friend whose personal information she already knew and did it in order to prove a point to Facebook.)