Yesterday I performed a clean install of my Windows 10 laptop (64-bit, Pro version) to get the Anniversary Update (#1607). I reformatted the partitions and everything, and went through the OOBE without any problems. But when I logged in with my local user account I noticed something very strange: Under C:/ Users/ there is now an additional user profile called "defaultuser0." I tried doing another format followed by a clean install, and again it was there.
Now here is where it gets really weird. I decided to go back to the previous version of Windows 10 (#1511) and again did a full format with clean install, using the Windows Media Creation tool I made a few months ago. It installs fine, but when I log in, guess what I see? This darn "defaultuser0" account! This was never here before. And yet, it somehow survives the whole process. Now today I have gone back and once again formatted the partitions of my laptop and have clean installed the Anniversary Update (#1607). STILL THERE...
What causes this? I am completely at a loss. I have spent well over a dozen hours trying to figure this out, and I have even called Microsoft's Tech Support, but so far I haven't found a satisfactory answer. I can still log in and use my laptop, but the rights and permissions on some folders belongs to this "defaultuser0" which is why I want to eliminate it. The whole purpose of a clean install is to avoid issues such as these. I did some research on Google, and have only found one or two results in German written by the user "M.Ziegler" but even these don't really solve the problem. A few users give some tips on how to delete the account through editing the registries and whatnot, but that's not really what I want. I know that one cannot simply erase every single trace of an account once it is created, and so I am trying instead to find a way to prevent it in the first place. How and why is it created? Am I just stuck with it?
Please, can somebody help me? I thank you in advance!
UPDATE on August 5th, 2016: This appears to be a bug which is only affecting some users. I spent more time testing it today, and even after deleting the account keys from the registry (as someone had suggested below) and completely removing "defaultuser0", it comes back is you ever run the DISM command string "Dism /Online /Cleanup-Image /RestoreHealth". What this seems to imply that this is actually a problem with the ESD/ISO, where it treats this as necessary even though it obviously isn't. Hopefully somebody will have a REAL answer for me soon.
UPDATE on August 6th, 2016: Microsoft's Level Two Technical Support called me back today. But even the elevated tech support staff has no clue on what causes this issue. The man I spoke to told me that because build 1607 is brand new, their manual doesn't have any details on this issue yet. Apparently they're researching the problem, but it could be weeks before a solution is found and put into their manual. I'll continue to post updates here when I have them.
UPDATE on August 27th, 2016: A quick shout out to the user "ChristopherButterfield", who in the comments below posted this link: https://social.technet.microsoft.com/Forums/en-US/3e7d85e3-d0e1-4e79-8141-0bbf8faf3644/windows-10-anniversary-update-the-case-of-the-mysterious-account-sid-causing-the-flood-of-dcom?forum=win10itprosetup While the link unfortunately does not contain a fix for the issue, it does highlight some aspects that I had previously missed, and thus confirms my suspicions that this "defaultuser0" negatively impacts system performance. Of particular note is an invalid SID that seems to be linked to defaultuser0: "...almost all the core components, have an Unknown Account with SID S-1-15-3-1024-1065365936-1281604716-3511738428-1654721687-432734479-3232135806-4053264122-3456934681" and, "All the core system COM objects seem to have this Unknown SID. And it seems that's the source of all the DCOM errors in the event logs." which is referring to Event ID 10016. More updates to come.
UPDATE on August 29th, 2016: I spoke to a man named Jeffrey today, who is another one of Microsoft's Level Two Technical Support staff. Unfortunately, there are still no known resolutions for this issue. I allowed him to remote access my laptop so I could show him exactly what I'm dealing with, and he made detailed notes which he promised would be passed along to Microsoft's technical engineers. He scheduled me for a callback on September 7th, and hopefully their team will have discovered a resolution for this error by that time. That's all for now. And please, if you have this same issue, click the "Me too" button, so they can see that it's affecting a lot of us and that it's worth their time to fix!
UPDATE on September 9th, 2016: Microsoft's Level Two Tech Support staff called me back on the 7th, as promised. However, the woman I spoke to was very dismissive and seemed to not know what I was talking about. As far as I can tell, nothing had been done. She told me to go see a specialist at the local Microsoft store, so I made an appointment for the following day so I could physically meet with one of their staff. So yesterday (the 8th) I went in and explained everything to "Andy B." and showed him exactly what was going on. He did a clean install with their own ISO, and surprise surprise, there was the dreaded defaultuser0. On a hunch, he went to go check something in the back. As it turns out, they have it on their OWN computers also; they just didn't realize it! With this knowledge in hand, he promised he would submit a full bug report using their own Microsoft Insights forum. Apparently, this is how they are able to communicate directly with Microsoft's software developers. Hopefully a patch will come from this, but who knows. The fact that Microsoft's own staff have this on their computers might encourage them to fix it sooner. More updates when I have them.
UPDATE on March 29th, 2017: My apologies for the long absence. To those of you who asked, yes, I eventually did just give up. I've had personal concerns to deal with, such as having to relocate to a new city and the death of a family member, and those things took priority. And honestly, I became so invested in trying to solve this issue, that it made me miserable and I had to stop for my own sanity. On the positive side, I've read that this issue should be resolved in the next major update, which is coming on April 11th, 2017. However, I haven't seen or heard official confirmation of this, so I would appreciate it if anybody could confirm this information from an official source. Additionally, I would love to know if this fix will be applied regardless of whether we upgrade to the Creator's Update from within the Windows Activation menu (that is, if we choose to keep all our files and programs), or if we will be forced to once again perform a complete clean install in order for the fix to really take effect. Thanks.