I have a quad 2.5 with 4.5 gb non ecc ram. Recently, I have noticed that activity monitor shows all of my cpus maxing out at random. to wit: cpu one will go green all the way while everything else is quiet. Then 2 or three of them will be at 30 to 50 percent, then a different one, say four, will max out...and so on and so on. Mind you, this is with no foreground apps running at all. Active process are
kernal task
pm tool
safari(to type this message)
vshield check
window server
Vshield check sows cpu usage at 100 percent
Force quitting it drops the idle cpu to normal.

Is it worth all this activity to run resident virus protection when mac has so few if any viri?