Have you had other accounts previously set up on your computer?
The long charactor code is the security code for a user whcih has been deleted in the past. Even though you may be an administrator, i believe (somebody correct me if i'm wrong), Mesh also set up an administrator account on the PC before it is shipped to you. That was should the PC go wrong and it be sent back to them, they can work on the system without requiring you to tell them all of your passwords etc.
It should be no big problem. You will not be able to delete the administrator account, nor the account that shows as a string of digits and numbers. They shouldn't cause a problem on your system though.
Is their any reason why you were running MBSA anyway? It is a business security tool mainly designed for analysing security on business networks.