Sorry but there might be a couple anti-virus's that slow your system down, but the majority are light on resources. My norton anti-virus takes up about 2 percent of my cpu when its running at 50 or 60 percent. In this day and age an antivirus is mandatory. Heck I thought everyone knew that. A simple light free edition of AVAST will do the guy a great job and his system won't be slowed down.