I don’t have the energy to write a lot about Facebook’s “shadow profiles”, the method of collecting information on people with the purpose of correlating them and finally assigning them to actual individuals. Preferably users, but there is no reason why Facebook would stop there.
Some time ago there were some articles about people being suggested as friends to each-other; they actually knew each-other but for legal / moral / domestic reasons they had kept their connection secret. For example, a sex-worker had used one phone number / email address etc. for private access to Facebook and another for her work-related, outside Faceboook, connections. Even so, she found herself and her clients being suggested as possible friends, on Facebook.
I didn’t doubt the shadow profiles had to do with that and this article examines an experiment to show how Facebook uses them.
Interesting to see how this works with GDPR.