Symptoms vary depending on the OS. Win9X systems are pretty much immune to some of these RPC exploitation viruses (Blaster, Welchia, etc) because they exploit an RPC hole in the security of NT based systems (2000, XP, etc). The symptoms run from a forced shutdown or reboot several minutes after the desktop loads, to complete system freeze during or immediately after the desktop loads. The only way around it is to boot in safe mode with Administrative log-on, apply the security patch, scan with a removal tool (or directly edit the system files manually and delete the bogus svchost files--big pain in the @$$!), then reboot. Before a solution was discovered, people had to boot from the install CD/boot floppies, run a Repair Install, then immediately apply the patches from Microsoft after successful booting (MAJOR pain in the @$$!).
It's a shame that the bulk of all the problems could have been prevented if everyone had updated their Winblows with the security patches Micro$oft released back in May-July. While it wouldn't have stopped the spread of the viruses, it would have at least kept them from crashing their systems.
If it ain't broke don't try to fix it! But, hell if you can tweak that bastard just a little bit more....hehehe.