This article is from the Miscellaneous Macintosh FAQ, by Elliotte Rusty Harold firstname.lastname@example.org with numerous contributions by others.
90% of all problems reportedly caused by viruses are actually
due to mundane bugs in software (and 90% of all statistics are made
up :-) ). Check your system with the latest version of Disinfectant,
3.6 as of this writing, by the excellent John Norstad from
Northwestern University. See
Disinfectant is absolutely free. It's easy to use and can
protect your system from most known Macintosh viruses. Releases
to protect from new viruses are normally made within a day or two of
the first confirmed sighting and capture of a new virus, and make
their merry way around the electronic highways faster than any
Macintosh virus ever has.
Unfortunately Disinfectant does not protect your system from what
have become the pernicious Mac viruses, Word Macro Viruses.
If you don't use Microsoft Word, you don't have to worry about
these. If you do use Microsoft Word, Microsoft offers a free
Macro Virus Protection tool which detects suspicious Word
files when they're opened and gives users an option to open the
file without executing the macros, thereby ensuring that a virus
does not execute. The tool can also scan your hard disk for one
Word macro virus, the Concept virus. It can not scan your disks
for other Word Macro viruses.
You may want to consider investing in one of the payware
anti-virals that will detect and destroy these sorts of viruses
such as Symantec's SAM, about $90 street price. At the least you
should download and use Microsoft's tool at