OK, so about a week after upgrading to SP3 on this computer, things started getting very slow. Dumb things like the cursor can't keep up with my typing and Firefox using 200MB of RAM for no reason. AVG Free 7.5 is reporting that the following files have been "CHANGED": kernel32.dll wsock32.dll user32.dll shell32.dll ntoskrnl.dll I have no idea what that even means, and AVG has been running for 3 days now without finishing, so I'm taking matters into my own hands. I've looked through the HJT logs and nothing seems out of the ordinary. I rarely ever use this computer, and certainly haven't downloaded any questionable software on it either. What gives?

Read this thread especially Response Number 2 by johnr. i_Xp/VistaUser

Thanks for the tip! I was able to get to the bottom of this pretty quickly, I should have realized this in the first place... The problem was not with any type of virus or malware: it was with the AV program itself. In the entire time I've been using Windows PCs, I've gotten ONE virus - and it was very recently when I found some old floppies containing DOS games from over ten years ago. That's it. Now, in that same time frame I've had countless problems with various AV/spyware packages. Norton and MacAfee were the all time worst. AVG works well on some PCs, others it inexplicably hogs resources (as was the case here). It has also become more and more bloated while not providing any better protection. I also used Ad-Aware for many years and it has met the same fate. The paranoid, X-Files conspiracy theory loving part of my brain is telling me it's all a scam. The AV companies are getting kickbacks from PC makers to intentionally write bad code and gradually slow down our computers to a crippling halt so that we buy new ones or install other worthless software packages on top of the ones that already don't work. I see three year old PCs in the trash all the time, it's nuts. From now on, I'm removing the AV software on all of my PCs and maybe I'll reconsider them once I foolishly prove myself wrong!