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Facebook friend finder is really creepy. It has suggested to me:

  • The father of a friend of mine—hose existence in Facebook was unknown to the said friend of mine himself.
  • The twin brother of a colleague of mine—of whose family I had no idea whatsoever about,
  • Close friends of a school-going young relative of mine—though I had no Gmail or any other web-based contact with the said relative for a long time.
  • An old and longstanding crush of a friend
  • Ex-girlfriend of a friend.

Additionally, I have lost count of the number of times when I first saw somebody's profile on Facebook through their twisted suggestion mechanism, and much, much later, came to know who the person actually is.

And many more.

I have no idea how on earth they find out all this connecting information. I have locked my security settings to the maximum. Nobody can find me on Facebook unless I go to them and add them as a friend. Then how is this possible? How does it work?

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I feel that some people let facebook log into their web email accounts, which would give facebook a collection of a bunch of email addresses that are associated in some way... so if someone has you and someone else in their address book, facebook could guess that you might know of each other. –  Daniel LeCheminant Jun 30 '10 at 20:43
    
I never thought the friend finder was that good, it mostly suggests people I don't know. –  David Z Jul 11 '10 at 3:49
    
You may not have met them yet; but you do move in similar circles. As I said I have lost count of the number of times in which I first saw a person in facebook friend suggestion, and later met that person in real life. –  George S Jul 11 '10 at 19:53

4 Answers 4

Facebook has access to all friendship-data on their site, even if you lock down the privacy settings. As an addition many users share their contact-book or even e-mails with Facebook. Most peoples have filled out their profile quite decent so it has data about your school, your employer, your current place, your interests and so on. Although Facebook states it does not use it, they can track all users (and even non-users) across many websites via the "like"-button which is transcluded directly from Facebook.

From this data it can calculate this friend requests.

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Even though your security settings are "locked down", Facebook still can use your friends list to find other people you may know. Other people may not be able to find you but Facebook can and will still use your information (such as your friend list). They cross reference your list of friends to your friends' friend list to find people you may know. There is probably some kind of complex algorithm behind who exactly they suggest. The algorithm probably checks for multiple friends in common, current location (for distance), similar groups, similar schools, employers, etc.

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I just created a new Facebook profile. I used a dummy email address to create the page.

Facebook then starts suggesting - GUESS WHO - myself, my gf, my sister and my closest friends as "people I might know".

Consequently, Facebook must go much deeper than just look at your friends and whose profile you are looking at - they seem to have monitored my IP address and connected the new Facebook profile to my old profile. Then they suggested myself and my friends.

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Did you clear all of your cookies first? Facebook keeps around some cookies even after you log out, which can tell them about a previously logged in user on the same computer. –  mark4o Dec 30 '11 at 8:38

I suspect that "stalking" and similar activities might also have an impact. In other words, if a person A repeatedly visits the public profile of another person B, then Facebook might deduce and suggest to B (and maybe even to established friends of B) that A is a friend.

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