According to a recent article[1], once an advertiser/attacker has collected a large quantity of email addresses, she can "import [them] as contacts" on Facebook

According to a recent article[1], once an advertiser/attacker has collected a large quantity of email addresses, she can "import [them] as contacts" on Facebook, thereby revealing which Facebook profiles they are associated with, if any. The article was written by a gentleman who wrote some early code for Facebook to do this which was later the subject of a Microsoft patent. Would it be fair to say that once a user submits an email address to a website, that website can locate the users Facebook profile, if one exists. No "Facebook Login" required. 1. https://www.washingtonpost.com/opinions/your-facebook-data-is-still-vulnerable-i-know-because-i-made-it-that-way/2018/04/13/1cf5c794-3e7d-11e8-a7d1-e4efec6389f0_story.html https://www.washingtonpost.com/opinions/your-facebook-data-i... Also, the curious reader may find these interesting, regarding the ease with which an attacker/website could learn a Facebook user's private friends list: https://www.telegraph.co.uk/technology/2018/04/17/facebook-quietly-stopped-apps-harvesting-users-private-data/amp/ https://www.telegraph.co.uk/technology/2018/04/17/facebook-q... https://gizmodo.com/how-facebook-figures-out-everyone-youve-ever-met-1819822691 https://gizmodo.com/how-facebook-figures-out-everyone-youve-... https://nakedsecurity.sophos.com/2013/06/23/facebook-issues-data-breach-notification-may-have-leaked-your-email-and-phone-number/ https://nakedsecurity.sophos.com/2013/06/23/facebook-issues-... https://www.facebook.com/notes/facebook-security/important-message-from-facebooks-white-hat-program/10151437074840766 https://www.facebook.com/notes/facebook-security/important-m... Finally, I have read that a major dating website has now removed Facebook Login.