'If ever there was a surefire way to sour users against a two-factor authentication system that was already highly flawed, Twitter has found it. On Tuesday, the social media site said that it used phone numbers and email addresses provided for 2FA protection to tailor ads to users.

Twitter requires users to provide a valid phone number to be eligible for 2FA protection. A working cell phone number is mandatory even when users' 2FA protection is based solely on security keys or authenticator apps, which don't rely on phone numbers to work. Deleting a phone number from a user's Twitter settings immediately withdraws account from Twitter 2FA, as I confirmed just prior to publishing this post.'

-- sources: https://arstechnica.com/information-technology/2019/10/twitter-used-phone-nu...

Cheers, Peter