Behind the Facebook profile you’ve built for yourself is another one, a shadow profile, built from the inboxes and smartphones of other Facebook users. Contact information you’ve never given the network gets associated with your account, making it easier for Facebook to more completely map your social connections.
Facebook needs to be de-privatized/open-sourced/heavily-regulated ASAP.
https://gizmodo.com/how-facebook-figures-out-everyone-youve-ever-met-1819822691
Curse anyone who ever imported their contacts into this faux-phishing behemoth.
I won’t even let their apps on my phone.