virus

1. A submicroscopic, non-cellular structure that consists of a core of DNA or RNA surrounded by a protein coat, that requires a living host cell to replicate, and that sometimes causes disease in the host organism (such agents are often classed as nonliving infectious particles and less often as microorganisms).Examples: "Under electron microscopy, a few viruses were seen floating near the cells."countableuncountable

2. (uncountable) A quantity of such infectious agents, considered en masse.Examples: "Not much virus was detectable on a nucleic acid test; the viral load was very low."; "Unless professionally inspected, they [plants] may also carry along unseen pests and diseases (particularly small insects and microbes such as virus or bacteria) whose populations might explode catastrophically in new locations."uncountable

3. (informal, metonymic) A disease caused by such an infectious agent; a viral illness.Examples: "He's got a virus and had to stay home from school."countableinformalmetonymicallyuncountable

4. (archaic) Venom, as produced by a poisonous animal etc.Examples: "Brazil, that inferno where every budding flower and every buzzing bluebottle fly bears a lascivious virus."archaiccountableuncountable

5. (computing) A type of malware which can covertly transmit itself between computers via networks (especially the Internet) or removable storage such as disks, often causing damage to systems and data; also computer virus.Examples: "Wait a minute! Is this one of those virus emails?!"countableuncountable

6. (computing, proscribed) Any type of malware.countableproscribeduncountable