Two-Factor Authentication Is Not The Problem
First, when a user gives Facebook their number for security purposes—to set up 2FA, or to receive alerts about new logins to their account—that phone number can become fair game for advertisers within weeks. (This is not the first time Facebook has misused 2FA phone numbers.)
But the important message for users is: this is not a reason to turn off or avoid 2FA. The problem is not with two-factor authentication. It’s not even a problem with the inherent weaknesses of SMS-based 2FA in particular. Instead, this is a problem with how Facebook has handled users’ information and violated their reasonable security and privacy expectations.