I got the little yellow shield this morning ... Two updates, one to prevent a stop error message and the other to download some kind of program to make sure you're running a "genuine" copy of Windows XP.
The only thing that gives me pause is that the "stop error message" thing hasn't been updated (according to Microsoft's site) since January, so I'm not sure why it's showing up now ... Maybe I'm just being paranoid, but is it possible that a virus/rootkit/whatever could actually override Microsoft's update system and make it look like you're installing legitimate updates when you're really installing all kinds of crap that you don't want?
According to Windows update, both of those are genuine patches. I pulled up the stop errors info and this is what I got.
Originally posted by Windows UpdateUpdate for Windows XP (KB900485) Date last published: 4/25/2006 Install this update to prevent an issue in which you may receive a “stop 0x7e in AEC.SYS” error message on a computer that is running Windows XP Service Pack 2. The error may occur during startup, or after the system has started. AEC.SYS is the acoustic echo canceling driver. After you install this item, you may have to restart your computer. http://support.microsoft.com/kb/900485
Vocatus atque non vocatus, Deus aderit. -- Erasmus
Thank you all for the help! After four days without home internet, our provider figured out it was something on their end. They said they would be trying some more stuff on Monday, so it might happen again, though.