Virüs

n. microorganism which functions as an infectious agent; computer program which is intended to be spread surreptitiously between computers and usually causes damage (Computers)

A virus (from the Latin noun virus, meaning toxin or poison) is a sub-microscopic particle (ranging in size from about 15–600 nm) that can infect the cells of a biological organism. Viruses can replicate themselves only by infecting a host cell. They therefore cannot reproduce on their own. At the most basic level, viruses consist of genetic material contained within a protective protein coat called a capsid. They infect a wide variety of organisms: both eukaryotes (animals, plants, protists, and fungi) and prokaryotes (bacteria and archaea). A virus that infects bacteria is known as a bacteriophage, often shortened to phage. The study of viruses is known as virology and people who study viruses are known as virologists. Viruses cause several serious human diseases, such as AIDS, influenza and rabies. Therapy is difficult for viral diseases as antibiotics have no effect on viruses and antiviral drugs are expensive. The best way to prevent viral diseases is with a vaccine, which produces immunity.
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Virus /vi·rus/ [L.] a minute infectious agent which, with certain exceptions, is not resolved by the light microscope, lacks independent metabolism [more]Virus - Community and Resources

Noun
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
(hypernym) microorganism
(hyponym) arbovirus, arborvirus
(classification) virology
(class) virion
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"
(hypernym) representation, delegacy, agency
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"
(synonym) computer virus
(hypernym) malevolent program

n. virus, microorganism which functions as an infectious agent; (Computers) computer program which is intended to be spread surreptitiously between computers and usually causes damage