I use AVG here too but there are some serious threats floating around lately.
I have been having problems with FireFox getting hit bad with malicious tracking cookies. Since typing this post here there have been 7 attacks of spyware that have been snagged by my Spyware Doctor and AVG running. I have removed Firefox now from my laptop because of this.
As for AVG being disabled, watch out for a new malware that has been circulating called XP Police. IT will attack your system and begin sending out your data to a remote IP address. I have no idea how this gets installed but it hit me this morning at 5:30 AM and by 7AM, I saw it was busy uploading all my C drive and had just begun to upload the first folder of the Documents and settings files when I pulled the ethernet cable.
This completely disabled AVG! Then it disabled my Task manager. I still have not been able to access my task manager but now have XP Police removed.
This damn spyware will cost me a half day trying to get rid of it. What a PIA!