"Facebook’s site says it gets information about its users “from a few different sources.”Facebook Doesn’t Tell Users Everything It Really Knows About Them - ProPublica
What the page doesn’t say is that those sources include detailed dossiers obtained from commercial data brokers about users’ offline lives. Nor does Facebook show users any of the often remarkably detailed information it gets from those brokers."
Monday, January 02, 2017
Facebook Doesn’t Tell Users Everything It Really Knows About Them - ProPublica
Also see How Facebook Learns About Your Offline Life (Technology Review)