Virus \Vi"rus\, n. [L., a slimy liquid, a poisonous liquid,
   poison, stench; akin to Gr. ? poison, Skr. visha. Cf.
   Wizen, v. i.]
   1. (Med.) Contagious or poisonous matter, as of specific
      ulcers, the bite of snakes, etc.; -- applied to organic
      poisons. [Archaic]
      [1913 Webster +PJC]

   2. the causative agent of a disease, . [obsolescent]
      [PJC]

   3. any of numerous submicroscopic complex organic objects
      which have genetic material and may be considered as
      living organisms but have no proper cell membrane, and
      thus cannot by themselves perform metabolic processes,
      requiring entry into a host cell in order to multiply. The
      simplest viruses have no lipid envelope and may be
      considered as complex aggregates of molecules, sometimes
      only a nucleic acid (DNA or RNA) and a coat protein. They
      are sometimes viewed as being on the borderline between
      living and nonliving objects. They are smaller than living
      cells in size, usually between 20 and 300 nm; thus they
      pass through standard filters, and were previously
      referred to as filterable virus. The manifestations of
      disease caused by multiplication of viruses in cells may
      be due to destruction of the cells caused by subversion of
      the cellular metabolic processes by the virus, or by
      synthesis of a virus-specific toxin. Viruses may infect
      animals, plants, or microorganisms; those infecting
      bacteria are also called bacteriophages. Certain
      bacteriophages may be non-destructive and benign in the
      host; -- see bacteriophage.
      [1913 Webster +PJC]

   4. Fig.: Any morbid corrupting quality in intellectual or
      moral conditions; something that poisons the mind or the
      soul; as, the virus of obscene books.
      [1913 Webster]

   5. (Computers) a program or segment of program code that may
      make copies of itself (replicate), attach itself to other
      programs, and perform unwanted actions within a computer;
      also called computer virus or virus program. Such
      programs are almost always introduced into a computer
      without the knowledge or assent of its owner, and are
      often malicious, causing destructive actions such as
      erasing data on disk, but sometime only annoying, causing
      peculiar objects to appear on the display. The form of
      sociopathic mental disease that causes a programmer to
      write such a program has not yet been given a name.
      Compare trojan horse[3].
      [PJC]

	

	virus
     n 1: (virology) ultramicroscopic infectious agent that replicates
          itself only within cells of living hosts; many are
          pathogenic; a piece of nucleic acid (DNA or RNA) wrapped
          in a thin coat of protein
     2: a harmful or corrupting agency; "bigotry is a virus that
        must not be allowed to spread"; "the virus of jealousy is
        latent in everyone"
     3: a software program capable of reproducing itself and usually
        capable of causing great harm to files or other programs
        on the same computer; "a true virus cannot spread to
        another computer without human assistance" [syn: computer
        virus]

	

	120 Moby Thesaurus words for "virus":
   acaricide, adenovirus, aerial infection, aerobe, aerobic bacteria,
   aerobic organism, airborne infection, amoeba, anaerobe,
   anaerobic bacteria, anaerobic organism, anthelmintic, antibiotic,
   antiseptic, autotrophic organism, bacillus, bacteria, bacterium,
   bane, being, bug, bug bomb, carbamate insecticide, carrier,
   chemosterilant, chlorinated hydrocarbon insecticide, coccus,
   communicability, contact poison, contagion, contagiousness,
   contamination, corruption, creature, cryptogenic infection,
   defoliant, direct infection, disease-producing microorganism,
   disinfectant, droplet infection, dust infection, echovirus,
   enterovirus, epidemiology, eradicant, filterable virus, fumigant,
   fungicide, fungus, genetic individual, germ, germicide,
   gram-negative bacteria, gram-positive bacteria, hand infection,
   herbicide, heterotrophic organism, indirect infection, individual,
   infection, infectiousness, insect powder, insecticide,
   living being, living thing, microbe, microbicide, microorganism,
   miticide, mold, morphological individual, nonfilterable virus, ont,
   organic being, organic chlorine, organic phosphate insecticide,
   organism, organization, pathogen, pesticide,
   physiological individual, phytogenic infection, picornavirus,
   poison, primary infection, protozoa, protozoon, pyogenic infection,
   rat poison, reovirus, rhinovirus, rickettsia, roach paste,
   roach powder, rodenticide, secondary infection, spirillum,
   spirochete, spore, staphylococcus, stomach poison, streptococcus,
   subclinical infection, systemic, systemic insecticide, taint,
   toxic, toxicant, toxin, trypanosome, vector, venin, venom,
   vermicide, vibrio, waterborne infection, weed killer,
   zoogenic infection, zooid, zoon

	

	virus n. [from the obvious analogy with biological viruses, via SF] A
   cracker program that searches out other programs and `infects' them by
   embedding a copy of itself in them, so that they become Trojan horses.
   When these programs are executed, the embedded virus is executed too,
   thus propagating the `infection'. This normally happens invisibly to the
   user. Unlike a worm, a virus cannot infect other computers without
   assistance. It is propagated by vectors such as humans trading programs
   with their friends (see SEX). The virus may do nothing but propagate
   itself and then allow the program to run normally. Usually, however,
   after propagating silently for a while, it starts doing things like
   writing cute messages on the terminal or playing strange tricks with the
   display (some viruses include nice display hacks). Many nasty viruses,
   written by particularly perversely minded crackers, do irreversible
   damage, like nuking all the user's files.

   In the 1990s, viruses became a serious problem, especially among
   Windows users; the lack of security on these machines enables viruses to
   spread easily, even infecting the operating system (Unix machines, by
   contrast, are immune to such attacks). The production of special
   anti-virus software has become an industry, and a number of exaggerated
   media reports have caused outbreaks of near hysteria among users; many
   lusers tend to blame _everything_ that doesn't work as they had
   expected on virus attacks. Accordingly, this sense of `virus' has passed
   not only into techspeak but into also popular usage (where it is often
   incorrectly used to denote a worm or even a Trojan horse). See
   phage; compare back door; see also Unix conspiracy.

	

	virus
     
         (By analogy with biological viruses, via SF) A
        program or piece of code written by a cracker that "infects"
        one or more other programs by embedding a copy of itself in
        them, so that they become Trojan horses.  When these
        programs are executed, the embedded virus is executed too,
        thus propagating the "infection".  This normally happens
        invisibly to the user.
     
        A virus has an "engine" - code that enables it to propagate
        and optionally a "payload" - what it does apart from
        propagating.  It needs a "host" - the particular hardware and
        software environment on which it can run and a "trigger" - the
        event that starts it running.
     
        Unlike a worm, a virus cannot infect other computers without
        assistance.  It is propagated by vectors such as humans
        trading programs with their friends (see SEX).  The virus
        may do nothing but propagate itself and then allow the program
        to run normally.  Usually, however, after propagating silently
        for a while, it starts doing things like writing "cute"
        messages on the terminal or playing strange tricks with the
        display (some viruses include display hacks).  Viruses
        written by particularly antisocial crackers may do
        irreversible damage, like deleting files.
     
        By the 1990s, viruses had become a serious problem, especially
        among IBM PC and Macintosh users (the lack of security on
        these machines enables viruses to spread easily, even
        infecting the operating system).  The production of special
        antivirus software has become an industry, and a number of
        exaggerated media reports have caused outbreaks of near
        hysteria among users.  Many lusers tend to blame
        *everything* that doesn't work as they had expected on virus
        attacks.  Accordingly, this sense of "virus" has passed into
        popular usage where it is often incorrectly used for a worm
        or Trojan horse.
     
        See boot virus, phage.  Compare back door.  See also
        Unix conspiracy.
     
        [Jargon File]
     
        (2003-06-20)