Facebook ignored a widely-known privacy flaw for years, allowing scammers, spammers, and other malicious parties to scoop up virtually all users names and profile details. Facebook had set the default setting for Who can look you up using the email address or phone number you provided? to Everybody The default setting was the weakest possible privacy: no privacy at all. Facebook chief Mark Zuckerberg acknowledged the scale of the problem in a Q&A with journalists: At some point during the last several years, someone has probably accessed your public information in this way”]
Source: https://grahamcluley.com/facebook-phone-search-lookup-privacy/