NT Authority System

I would like to know What NT Authority System is??? I have just removed the Blaster worm from an XP system. Connected to internet to download the patches for XP, while on Microsoft site and looking through all the downloads a message popped up saying the computer would be shut down. Message said “Remote Proceedure Call Terminated Unexpectedly by NT Authority System” Tried a couple of times and same thing. Also what is the correct security Patch to stop the XP worm as there are so many downloads, but can’t stay on internet long enough to get the patches. I am sure I have removed the Blaster Worm correctly as done in Normal Windows and also in Safe Mode. Both occasions said Blaster Worm has been removed and so many files have been removed/added.
Any ideas thank you