This article is from the Viruses and the Mac FAQ, by David Harley D.Harley@icrf.icnet.uk with numerous contributions by others.
* Change Detectors/Checksummers/Integrity Checkers - programs that
keep a database of the characteristics of all executable files on a
system and check for changes which might signify an attack by an
* Cryptographic Checksummers use an encryption algorithm to lessen
the risk of being fooled by a virus that targets that particular
* Dropper - a program that installs a virus or Trojan, often
* Generic - catch-all name for antivirus software that doesn't know
about individual viruses, but attempts to detect viruses by
detecting virus-like code, behaviour, or changes in files
containing executable code.
* Heuristic scanners - scanners that inspect executable files for
code using operations that might denote an unknown virus.
* Monitor/Behaviour Blocker - a TSR that monitors programs while
they are running for behaviour which might denote a virus.
* Scanner (conventional scanner, command-line scanner, on-demand
scanner) - a program that looks for known viruses by checking for
recognisable patterns ('scan strings', 'search strings',
'signatures') or using a more flexible algorithmic approach for
detection of polymorphic viruses, which can't be found by a search
for a simple scan string. These are not usually associated with the
Macintosh platform, but there are Word Macro viruses which exhibit
* Trojan (Trojan Horse) - a program intended to perform some covert
and usually malicious act that the victim did not expect or want.
It differs from a destructive virus in that it doesn't reproduce,
(though this distinction is by no means universally accepted).
* Virus - a program (a block of executable code) that attaches
itself to, overwrites or otherwise replaces another program in
order to reproduce itself without the knowledge of the computer
user. Most viruses are comparatively harmless, and may be present
for years with no noticeable effect: some, however, may cause
random damage to data files (sometimes insidiously, over a long
period) or attempt to destroy files and disks. Others cause
unintended damage. Even benign viruses (apparently non-destructive
viruses) cause significant damage by occupying disk space and/or
main memory, by using up CPU processing time, by introducing the
risk of incompatibilities and conflicts, and by the time and
expense wasted in detecting and removing them.