Unknown Accounts in User Security

While troubleshooting an Exchange issue, I noticed that any new user that I create in our domain includes two "Account Unknown" entries in their security tabs.  SIDs are:


I was prepared to clean all unknown SIDs from our domain using the tool found here (https://gallery.technet.microsoft.com/How-to-remove-all-unknown-9d594f3a) but noticed that these two SIDs appear frequently.  I ran the following command to pull info from the SID but don't understand anything additional from it:

 PS D:\temp>> [wmi] "Win32_SID.SID='S-1-5-21-[DOMAIN]-4703'"

__GENUS              : 2
__CLASS              : Win32_SID
__SUPERCLASS         :
__DYNASTY            : Win32_SID
__RELPATH            : Win32_SID.SID="S-1-5-21-[DOMAIN]-4703"
__DERIVATION         : {}
__NAMESPACE          : root\cimv2
__PATH               : \\DOMAINCONTROLLER\root\cimv2:Win32_SID.SID="S-1-5-21-[DOMAIN]-4703"
AccountName          :
BinaryRepresentation : {1, 5, 0, 0...}
ReferencedDomainName :
SID                  : S-1-5-21-[DOMAIN]-4703
SidLength            : 28

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Can somebody identify what these would be?  Are they safe to delete?  Thanks in advance!
Dan CarpIT DirectorAsked:
Who is Participating?
Will SzymkowskiSenior Solution ArchitectCommented:
These are accounts that have been removed from the domain but had Security ACL's set at the top level. That is why when you create new users these accounts that inheriting permissions on all new accounts. You can safely remove them.

You will need to remove them from the source where it is being inherited.

Dan CarpIT DirectorAuthor Commented:
Thanks Will!  I found these two accounts in our top level domain security properties.  After removing them from this location, new users no longer inherit them.  For existing users and objects who have these still embedded, would you use the powershell script I referenced above or do you have another suggested method to wipe old accounts?  Very much obliged!
Will SzymkowskiSenior Solution ArchitectCommented:
Typically you could script this but it would take a lot of work in regards to creating a script that will work for all locations, AD File Shares etc. Best thing to do is just be cognizant when you come across an account that is shown just using the SID you can remove them.

Dan CarpIT DirectorAuthor Commented:
Very quick and helpful answer - thanks Will!
Will SzymkowskiSenior Solution ArchitectCommented:
Glad to help!

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