Strange SID appearing under user security

[Migration User]

Recently I have been going through a class that teaches how to operate windows 7 , and we covered permissions. I decided to try it out on my own computer and I saw a random SID with a red ? on the person, that was not apart of my user list. It then suddenly dissapeared like a cocaroach from the light, and it has me concerned about my security. New Picture.jpg Someone help. None of my instructors knew what it was, and they are heavily certified professionals...

[Migration User]

Not even curious? :/

 

[SMLatCST]

Erm, I don't really see how this relates to SNAC tbh, as it is entirely a windows function you're talking about here.

It's fairly common to have that sort of thing appear if you've given another domain user explicit rights to a folder, and the user is later deleted from AD.  This can cause an orphaned SID entry in the folder permissions (i.e. windows can't link the SID to an account and resolve its name anymore).

If concerned because of the disappearing entry though, I'd recommend you contact Microsoft support.