Should I be worried about an Unknown Account in my system files?

In C:\Users Sammy
in the Security tab there are Accounts for

SYSTEM
Sammy (Sammy-Six\Sammy)
Account Unknown (S-1-5-21-142667727-3232057827-3827426010-1006)
Administrators (Sammy-Six\Administrators)

All Accounts were set to Allow everything - except
None of the Accounts were Allowed Special Permissions

when I realised this...

I Denied everything to Account Unknown.

I am Sole User.

This Unknown Account is NOT present in the Security section of either Guest or Public Users.

Hello Sammy,

An "Unknown" account with it's SID number showing like that in permissions (Security tab) is from an account that is no longer available (ex: from remote PC or USB drive with files from another PC) or has been deleted.

If you like, you can safely remove the account from the list in permissions. :)

Thank You, Brink.

You have set my mind at ease...

I use a 'dock' with my Netbooks... a Ziboo Zipad Netdock with built in DVD burner and Hard drive (plus 2 extra USB Ports)... That must be where the Account 'came from'

Again... Many Thanks for your timely advise

You're most welcome Sammy. :)