[michaelt]

IIRC the way Facebook's "platform" stuff worked was that when one user authorized an application, it got to see all their friends' data. Farmville had to be able to access your friends list to see who you could send a sheep to, you see.

Nowerdays this seems like an incredibly dumb idea, sure, and personally I disabled it entirely the moment it came out. But we can cut them some slack, because back in ~2006 facebook was a new thing, for young people - and nobody was sure where this new "social media" thing was going to go.

On top of that I believe Cambridge Analytica did the usual "personality test" trickery where you fill out a survey, then it won't show your result until you hand over your details and accept some legal mumbo-jumbo.

So your Great Uncle wanted to know what harry potter character he was, clicked a consent button, and Cambridge Analytica got your PII.