Add “a phone number I never gave Facebook for targeted advertising” to the list of deceptive and invasive ways Facebook makes money off your personal information. Contrary to user expectations and Facebook representatives’ own previous statements, the company has been using contact information that users explicitly provided for security purposes—or that users never provided at all—for targeted advertising.

Shadow Contact Information

Second, Facebook is also grabbing your contact information from your friends. Kash Hill of Gizmodo provides an example:

…if User A, whom we’ll call Anna, shares her contacts with Facebook, including a previously unknown phone number for User B, whom we’ll call Ben, advertisers will be able to target Ben with an ad using that phone number, which I call “shadow contact information,” about a month later.

This means that, even if you never directly handed a particular phone number over to Facebook, advertisers may nevertheless be able to associate it with your account based on your friends’ phone books.

Nice going FaceBook.. I don’t give you my phone number so you just grab it from a friend’s address book.

Source: You Gave Facebook Your Number For Security. They Used It For Ads. | Electronic Frontier Foundation