Facebook Is Giving Advertisers Access to Your Shadow Contact Information

Another in the endless series of findings on how Facebook uses your data to target you.

I was helping him test the theory by targeting him in a way Facebook had previously told me wouldn’t work. I directed the ad to display to a Facebook account connected to the landline number for Alan Mislove’s office, a number Mislove has never provided to Facebook. He saw the ad within hours.

They are even doing this with data you give them for security purposes.

They found that when a user gives Facebook a phone number for two-factor authentication or in order to receive alerts about new log-ins to a user’s account, that phone number became targetable by an advertiser within a couple of weeks.

The EFF highlighted this terrible use of security information for advertising targeting as well.