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Out of curiosity and astonishment. I just got a Facebook friend request from a fellow German-speaking SO user. I was suggested by his "friend finder" function but I have, with 99.9999999% certainty, never been in any kind of contact with this user, neither E-Mail nor otherwise. The only exception being Stack Overflow: I have had several friendly discussions with that user in comments, and possibly have answered one or two of his questions.

I'm interested to understand how they pulled this off? Does anybody know whether Facebook parse sites like SO for conversations in order to suggest new contacts?

Note that I have no problem with the friend request, nor with Facebook if they're actually doing this - SO conversations ares all public data after all. I am just astonished. Or does anybody have some other idea how this could have happened?


  • I am not involved with that StackOverflow group that exists on FB, nor with any other SO related activity there

  • I am signed up on Facebook with the same E-Mail address as I am on SO, so it is possible for FB to identify my SO account by gravatar

  • I have only one SO related Facebook contact, and he is not friends with this other user

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Your email is publicly available here. If I put that into Facebook's search, I get you as a result. Am I missing what the mystery is here? Perhaps the user added you to their contacts for the heck of it? Or just added you on Facebook?

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It was the FriendFinder that suggested to @Pekka to add him, not the other SO user who added @Pekka. – systemovich Mar 1 '11 at 10:45
@Geoffrey actually, it was the other user who got me as a suggestion, but he did not actively search for me and there was no reason for his friend finder to suggest me, as we have no connection whatsoever beyond a bit of chatting on SO. – Pëkka Mar 1 '11 at 15:17
Doesn't the Friend Finder just do searches based on matches in your contacts? So if the user had added Pekka as an email contact, and then did Friend Finder...? – Rebecca Chernoff Mar 1 '11 at 15:30
@Rebecca but that's the point. The user had not added me as an E-Mail contact. He had no reason to look for me, but there I was. My question is why (Facebook are known to use all sorts of privacy-disregarding algorithms in Friend Finder, but this seems weird. I am not 100% excluding the possibility that there is some other explanation for this like the one given by @Geoffrey but it looks unlikely) – Pëkka Mar 1 '11 at 15:39
@Pekka, are you sure you weren't added as an email contact or are you guessing? Just seems to be the most logical answer. shrugs – Rebecca Chernoff Mar 1 '11 at 15:44
@Rebecca I was contacted by the user, who claimed Friend Finder had listed me, and wondered why. I can't prove it, but I have no reason not to believe him. I agree being in his E-Mail contacts is the most logical answer but it doesn't look like it's the case. I will look into whether he is a friend of a friend, though – Pëkka Mar 1 '11 at 15:46

He probably is a friend of a friend.

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I will look into this, good point. – Pëkka Mar 1 '11 at 15:19

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