mac rootkit

I think I have a mac rootkit.  When I opened activity monitor I noticed finder jumping around.  I installed the latest updates and restarted.  I see in activity monitor something open up and close instantly.  I don't know what to do about it.  Can someone help me.  I don't know if Norton Internet Security supports PC or Mac rootkits.  Will a wipe and reload help?  And if it is on a USB drive.  What then?  Do I format the USB drive?  Do I backup anything to disc or not?