Definately do a full virus scan. My Norton is always active. I have set it to automatically do a scan once a week. Since I am a night person, I have it set to run a FULL SCAN every Friday at Midnight (saturday morning). While I am using the computer it will kick in. Sometimes I do not even notice but other times it may slow things down a bit. Main point, it does not have to stop you from working. It scans in the background. Remember though to select a scan time that will be at a time when your computer will be on. If your computer is off at that time, it will not perfom the scan. I choose the time that I did since it is a time that I am almost always on the computer.