Started the computer and got a dialog box (before even the login screen appeared): "lsass.exe - Systemfehler. Ein ungültiges HANDLE wurde angegeben." (system error - an invalid HANDLE was specified).
Oops, thought I. Sasser worm? Got through my firewall?
After I clicked OK, the computer rebooted—and appeared to act fine so far. Hit Wikipedia for the article, which indicated that the Sasser worm usually leaves a file C:\WIN.LOG or C:\WIN2.LOG, neither of which I had. Downloaded Stinger and ran that.
Stopped it when it ran into the tarpit that is 42.zip (a carefully crafted recursive ZIP of ZIPs that, if you were to unfold it completely, would run into zillions of bytes to scan); removed the bit to check in archives and re-started it. (Nothing so far, but it's still running.)
I'll have to think what to do about that file. Maybe password-protect it or something; it's always a bit annoying when some scanner decides to walk through it, because that takes forever.
Also googled for the error message (in German, since that's all I had) and found a few support forums where people had posted with that same error, asking for advice. Those forums appeared to consist mostly of the blind leading the blind—people saying "lsass.exe is the Sasser worm! Remove it!" and the like. And a couple of people saying that the only thing that had helped them was a repair installation of WinXP, which sounded more plausible but isn't something I'd like to do, especially since all I have is a recovery CD and I can imagine it doesn't have a "repair install" option but will return the system to its initial state—sans pne's files. Whoop.
(That reminds me—ought to back up some of my files sometime. *cough* I'm still waiting for empty DVDs to use for that; backing up to CDs would just need way too many.)