For example, Facebook recommends me a friend:

  1. We really know each other
  2. We do not have mutual friend on Facebook
  3. We both have whatsapp and have each other's phone number, but never chat on whatsapp before. Or we are in the same whatsapp group only. Does FB use whatsapp contacts as reference?
  4. We are not friend on any social media apps, twitter, IG, etc.
  5. We are from the same university, but graduate year differ in several years. And there are so many students...
  6. I use Android phone, and I never sync my contacts online.

It happens several times to recommend a correct friend.

I feel curious, in this case, what's the data source used by FB's algorithm to recommend a likely friend?

closed as off-topic by Overmind, Steffen Ullrich, schroeder May 2 at 11:31

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question does not appear to be about Information security within the scope defined in the help center." – Overmind, Steffen Ullrich, schroeder
If this question can be reworded to fit the rules in the help center, please edit the question.

  • 1
    I think it may be related to privacy, part of my privacy research project. – TJCLARK May 2 at 7:57
  • 2
    I think your third point answers the question.Whatsapp is owned by facebook. – Vipul Nair May 2 at 8:00
  • 4
    Facebook is famous for shady practices and doesnt give a hoot about their user's privacy.They have much more information than your contacts.This question is better suited for data science or facebook employees (if they are willing to answer that is) – Vipul Nair May 2 at 8:05
  • 1
    I actually got a recommendation for someone I have known a while, with no mutual friends, the night THEY added my phone number to their phone....coincidence? maybe, but probably not. tin foil hattery. I have never willing given FB my phone number, but I know for a fact they have taken it. – TheHidden May 2 at 8:31
  • 3
    It may be because this friend viewed your profile – paj28 May 2 at 9:41

There are many possible use cases for this. Some of them are

  1. Location data - You told that you know this person. Both of you might have been in the same location many times.
  2. Contact Info - You have never synced your contacts online, but the other person might have. He did have your contact information.
  3. Same University - As you told, you both are from same university.
  4. Profile views - As paj28 said in comments, he might have viewed your Facebook profile.

Does FB use whatsapp contacts as reference?

No. According to WhatsApp website, They share some information including phone numbers, preferences, etc... with Facebook. But they don't share your contacts and other information.

Importantly, WhatsApp does not share your WhatsApp contacts with Facebook or any other members of the Facebook Companies, and there are no plans to do so. WhatsApp also does not share your messages with Facebook

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