[JD557]

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.

[caseysoftware]

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.