My business partner and I have separate accounts, separate email addresses, separate profiles, across several StackExchange sites. Mysteriously, we now see that his account was merged into mine.
What's particularly scary is that we can both login to the same account using our individual Google accounts. His user name is "Quant Guy". We never use the same computer and would never give each permissions to the others account.

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    Wow. On the Quant site "your" account has 0 answers and 0 questions, yet the bounties tab show you got two which are actually his. Some kind of bizarre half-merge? I'm adding the bug tag too. – Matthew Read Dec 19 '11 at 18:50
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    Auto-merge is scary. Or maybe I'm the .0001% of cases where it goes bad? =) – SFun28 Dec 19 '11 at 18:52
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    This is troublesome, I work for a large software game development company and we have several hundred people using SO from the same work IP daily. I really hope this isnt an automated process based on the source IP of users. – chown Dec 19 '11 at 18:55
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    Auto-merge sounds like a worse idea than regex HTML parsing and curse filters combined. – Ben Brocka Dec 19 '11 at 19:40
  • i got the same problem .. me and my friend account was merged but the problem is he can access but i am not ... its like my account has been deleted – Mohammad Fahmawi Dec 21 '11 at 15:28

One of you logged into the site while still logged in as the other user, this attempts to add that OpenID credential to your account, and since an account with that credential already exists on another, it initiated a merge.

In the future don't login over top of each other, you've just been the lucky winner of guinea pigging our new unmerge process, enjoy.

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    Nick - I appreciate the help. Two issues: 1. We both lost a bunch of points (my biz partner was a top user in Quant Exchange and Economics) 2. we never logged in on top of each other. – SFun28 Dec 19 '11 at 18:55
  • @SFun28 Never shared the same computer? – Matthew Read Dec 19 '11 at 18:57
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    Aside from the massive loss of points, it seems I still have 2 bounties from Quant Exchange that are my business partner's, not mine. In no world could I earn a bounty related to finance, I'm a coder! =) – SFun28 Dec 19 '11 at 18:58
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    @MatthewRead - no. sharing a computer is bad practice =) – SFun28 Dec 19 '11 at 18:58
  • In another question about merged accounts, the asker stated: "[the system] then saw I had 2 accounts and asked to merge and sync". Do you think the user was prompted this time as well? – Arjan Dec 19 '11 at 18:58
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    We were never asked such a question. Quant Guy was viewing Quant Exchange this morning. This afternoon he refreshed and saw that he was now me. – SFun28 Dec 19 '11 at 19:00
  • Any chance a badly configured caching proxy might have messed up, @SFun28? (Maybe if a caching proxy serves content to the wrong computer, cookies and stuff might get mixed up badly? I guess not, but proxies can mess up, and maybe some stackauth.com data got messed up?) – Arjan Dec 19 '11 at 19:07
  • Arjan - My network knowledge is limited, but our setup is pretty simple - we have a dlink wireless router and a switch to extend the number of ports available. We don't have a caching proxy, but perhaps the router or switch is doing some caching? – SFun28 Dec 19 '11 at 19:15
  • Please tell me this isn't an IP level feature. – Ben Brocka Dec 19 '11 at 19:41
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    @Ben - It has nothing to do with IPs, the users in question logged in on top of each other in the same browser, with an email that was on the other's account. – Nick Craver Dec 19 '11 at 19:44
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    @SFun28 - I don't understand why you've accepted this answer. If you actually believe you are correct and have never logged in on top of each other, then there is presumably something else going on, and this answer is quite wrong. – ire_and_curses Dec 20 '11 at 18:00
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    @ire_and_curses - they logged in on top of one another, we can see this in the traffic logs, this generated a queue items developers look at and approve or reject for account merges...in this case it appeared to be a dupe account, that wasn't the case....which is why we built unmerge in the first place, mistakes happen. – Nick Craver Dec 21 '11 at 15:10
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    @Nick Craver - I understand clearly that you are quite sure that's what happened. But the OP was equally clear in telling us that's not what happened, and that as far as he was concerned, it couldn't have happened. There is some ambiguity surrounding proxies etc. You didn't respond to any of those comments. So it's your opinion against his. Which means if he truly believes his own story, he can't in good conscience accept yours. So he shouldn't tick your answer. What I happen to think is the truth is quite irrelevant. – ire_and_curses Dec 21 '11 at 15:57
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    @ire_and_curses - It's not an opinion...it's hard evidence based on log data, if it were a proxy issue this wouldn't be a one-time occurrence, and their traffic would look quite different. I'm not saying he should accept this answer...I was explaining exactly what happened in order to help the user, that's all. This isn't the first of these we've seen, nor will it be the last I'm sure. – Nick Craver Dec 21 '11 at 16:03

This will probably be because you both frequently browse the site from behind the same router, giving you the same IP address. There might be an automatic merge of accounts that use the same source IP for some percentage of their requests.

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    We work in the same office behind a single router, so that is correct. I imagine lots of people have this setup. – SFun28 Dec 19 '11 at 18:50
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    And: lots of students who're using school computers. – Arjan Dec 19 '11 at 18:52
  • I have no other idea, this is the only reason I can think of for this to happen. They might also do other checks like what browser and os you use, no idea if i'm correct tho. – bigblind Dec 19 '11 at 18:53

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