Rundll32.exe 100 cpu usage and avg finds virus after scan norton

Hello everybody,

I have a problem with my computer (64 bits system windows 7 norton internet security 2010) since a week ago a had a problem with my pc because it was running at 100 % cpu , i checked my task management and i saw the rundll32.exe was running at 1000000 kb  so i killed it .

My question : after this accident i wondered how this happened by visiting multiple sites and forums.

I also downloaded AVG and first i runned a system scan by norton... yeah no viruses and cookies (wich is weird)

system scan avg : 5 trojan horses and droppers and more then 21 cookies...wtf:smileysad:

This is very dissapointing because i dont know when i have a virus or not ...the trust of norton is now gone...

I was wondering if i could be wrong??? Is this a flaw??? I dont know ... and the problem of my cpu is still there...