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If some of your contacts have this enabled then they can rebuild the network.

There was a case not so long ago where unrelated patients of a psychiatrist were suggested as friend to each other. The only possible link is that they all had the psychiatrist in their contact or vice-versa. The friending suggestion by itself was an outing of private medical information.

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My wife is a private practice speech therapist. She goes to great lengths to separate her personal social media from work social media. She has separate work and personal accounts for Facebook, Google, WhatsApp etc. Still she gets friend suggestions for her clients on her personal accounts. And it's not just once or twice, usually her suggested friends list is almost the exact same as her current client list.

Its creepy, and slightly disturbing to realise just how much effort they are putting in to mapping out your life and acquaintances even when you try to prevent it.

That's possible. People are probably giving Contacts permission to Facebook without thinking twice.

Although I recall a comment by a Facebook engineer about how they link users based on their IP addresses. So if you and your coworker are connected to the same WiFi at work Facebook can easily figure out that you both work at the same place.

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