Facebook Is Giving Advertisers Access to Your Shadow Contact Information


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“Facebook is not content to use the contact information you willingly put into your Facebook profile for advertising. It is also using contact information you handed over for security purposes and contact information you didn’t hand over at all, but that was collected from other people’s contact books, a hidden layer of details Facebook has about you that I’ve come to call “shadow contact information.”

“I think that many users don’t fully understand how ad targeting works today: that advertisers can literally specify exactly which users should see their ads by uploading the users’ email addresses, phone numbers, names+dates of birth, etc,” said Mislove. “In describing this work to colleagues, many computer scientists were surprised by this, and were even more surprised to learn that not only Facebook, but also Google, Pinterest, and Twitter all offer related services. Thus, we think there is a significant need to educate users about how exactly targeted advertising on such platforms works today.”