In this land of 3Ghz processors I am not at all worried about giving up a few cycles to my antivirus in addition to the 10mb of ram it elects to use. In addition the comment about the only way a person can get a virus from the internet is blatantly false as you can get a virus from any shared media. Those sources include cd-roms, usb flash drives, floppys ... etc. If your computer runs any flavor of Windows you would be wise to run antivirus.