This in the DOS days was king supreme.  FRISK Software was founded in 1993 by Fridrik Skulason, who first developed the popular F-PROT Antivirus (for DOS) in 1989 and the world\’s first heuristic behavior scanner in 1991.  Though he got his first virus definitions from John McAfee, he developed a superior product that even then was free for home users.  Since windows came around, I have kept watch on the F-protect line, but it has yet to win me over as the primary contender.