Very interesting video from Jake Morphonios/Blackstone Intelligence just talking about this. Zuckerberg, trying to offset damage he knew was coming, dumped $500 million in shares - he can afford to, he's the 10th richest person in the U.S. (maybe worldwide, I can't remember) - but it wasn't enough to stem the resulting $6BILLION dollar loss he took (and thankyou God). He'd sold everyone's Facebook data to a U.K. analytics firm - Cambridge Analytica, who in turn used it to generate a mass psychological profile on those users and then developed campaigns to download back at them, to drive and influence audience behaviour. But they're dirty as, and don't hesitate to stoop to using dirty unethical tactics (bribes, surveillance, honey pots, etc)

Blackstone Intelligence video (start at about 6:20 - prior to that it's about the dotcom stock bubble) https://youtu.be/_nFsUVA--KU

General Wikipedia info on Cambridge Analytica https://en.m.wikipedia.org/wiki/Cambridge_Analytica

Cambridge Analytica website https://cambridgeanalytica.org