The IEEE ran a piece a couple of years ago on how facebook (and others) can computationally work out things about non–facebook users, including habits, interests and even probable place of residence, from the info provided by their users.
Twitter started emailing me all kinds of technical EU political stuff when I took a job there, even though I’m not on twitter (although my company, corrupt press, is). I’m actually rather grateful to them for that, since they bought it home to me what any organisation with dosh and wit could do, and thus will have done.
Privacy is dead; we’re living in Marshall McLuhan’s global village, where everyone can know what everyone else is up to. Well, right now, no, it’s where the rich few can know what everyone else is up to. I seem to be coming to the opinion that the information shouldn’t be just in the hands of the industrial aristocrats or the dark state, but available to everyone; a democracy of secrets.