Solved unknown User S-1-5-21 xxxx in Folder properties

[Major76]

Hi There,

I'm new to the forum so Hi all

OS: Win 7 Home SP1

Recently discovered in the security properties of certain Folders/files have 4 x unkown user 'S-1-5-21 xxxx'
I am able to remove the unknown users, but there are far to many folders to manually remove from all.
Am curious to know if this is some kind of security risk? and is there an easier way of removing the users?

Also noticed if I create a new document within 'documents' in my library then the 4 unknown users appear in security properties?
Yet if I create a document on my desktop I only get sytem/user/admin users created. if i then copy this to 'Documents' Folder in 'libraries' again the 4 'unknown user s-1-5-21 xxxx' are present in security user group?

I have run several thorough virus/malware checks but found nothing?
Also have not created any users apart from my own and am not part of any Domain.

Any help regarding would be much appreciated as after searching the web am seeing conflicting advise.

 

[Major76]

Quick update. Have now removed the unknown users from the parent folder 'My Documents' found in libraries. This has removed all unknown users from folders/files found in 'libraries\documents' so problem solved.

Would still like to know where these unknown users originated from though?