See Facebook "shadow profiles", data collected on persons either through third-party activity (though the profiled individual is on Facebook), OR on persons not using Facebook at all.
https://theconversation.com/shadow-profiles-facebook-knows-a...
https://www.dailydot.com/unclick/facebook-shadow-profiles-pr...
https://en.wikipedia.org/wiki/Shadow_profile
See Facebook "shadow profiles", data collected on persons either through third-party activity (though the profiled individual is on Facebook), OR on persons not using Facebook at all.
https://theconversation.com/shadow-profiles-facebook-knows-a...
https://www.dailydot.com/unclick/facebook-shadow-profiles-pr...
https://en.wikipedia.org/wiki/Shadow_profile