Facebook Is Using Your Two-Factor Authentication Phone Number to Target Advertising
Schneier on Security
OCTOBER 2, 2018
From Kashmir Hill : 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.
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