I don't have a Facebook account (never did) but eventually "had" to create an Instagram account.
I was baffled when I saw their recommendations: They recommended me some old classmates and my university without having any direct interaction from me.
I understand how cookie syncing/matching works and I know Facebook probably knows a lot about me even without an account, but that still got me by surprise.
It's not just that.. anyone you know who ever imported their contacts list would be connected to you. With enough data points about them, FB/IG can infer quite a few things about you pretty easily.
If your university's alumni association imported their contact list, it's even worse.
I was baffled when I saw their recommendations: They recommended me some old classmates and my university without having any direct interaction from me.
I understand how cookie syncing/matching works and I know Facebook probably knows a lot about me even without an account, but that still got me by surprise.