The difference between "hostile" executables (such as
viruses) and others is academic, when a root-account
user can already shoot off his foot or other vital
parts, with one of myriad, brief commands. Put the
other way, the same survival skills by which you, as
a novice sysadmin, will cease destroying your system
directly will also, more generally, dissuade you from
doing unwise things as root, thereby incidentally
keeping viruses and their kin off your system.

        -- Rick Moen