All of my desktop computers (all running XP), and my server randomly have the OS shutdown occur without warning. It starts happening in the early afternoon around 1:30-ish. I have done malware and virus scans on all of the computers. The OS is shutting down. This is not a power loss issue/power supply problem.
I have also re-installed XP on two of the computers and did not join them back to the domain. The also performed unprovoked shutdown of the OS.
I modified the Local Policy to not allow Shutdown from any user. It still happens.
Since the clean computers are doing the same, I assume that this is happening from a remote entity (LAN or WAN).
I'm looking for suggestions as to where to go from here.