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Facebook asks users to add their phone numbers for 2-factor authentication, then misuses that info to target ads. Researchers at Northeastern uncovered this by signing up as an advertiser and finding many clever tricks to reverse-engineer FB's targeting. mislove.org/publications/P… 
That's just one of five types of PII misuse they uncovered. Worse, Facebook doesn't disclose to users that it does this and there's no way to prevent your phone number from being used for ad targeting, even by removing it from your account.
Worth highlighting: one of the many ways Facebook can get your phone number is if it's in _someone else's_ phone contacts. Facebook will then use that to let advertisers target ads to you, connect your online and in-store purchases, etc.
This paper has just won a Best Student Paper Award at the Privacy Enhancing Technologies Symposium in Stockholm! Another paper, *also* about the creepiness of FB's ad targeting, was runner-up for the Best Paper Award: ftc.gov/system/files/d…
Quite the dubious distinction for FB.
Quite the dubious distinction for FB.
As a reminder, there's no opt out from big tech. Facebook can and does surveil you even if you never signed up because of your "friends" who did. Tracks you as you browse the web. Is embedded in thousands of mobile apps. Buys your data from data brokers.
If you're planning to reclaim your privacy by quitting Facebook, don't forget these six other steps 😉
