virus

A computer virus is a computer program that can replicate itself and spread from one computer to another. The term "virus" is also commonly, but erroneously, used to refer to other types of malware, including but not limited to adware and spyware programs that do not have a reproductive ability.

Malware includes computer viruses, computer worms, Trojan horses, most rootkits, spyware, dishonest adware and other malicious or unwanted software, including true viruses. Viruses are sometimes confused with worms and Trojan horses, which are technically different. A worm can exploit security vulnerabilities to spread itself automatically to other computers through networks, while a Trojan horse is a program that appears harmless but hides malicious functions. Worms and Trojan horses, like viruses, may harm a computer system's data or performance. Some viruses and other malware have symptoms noticeable to the computer user, but many are surreptitious or simply do nothing to call attention to themselves. Some viruses do nothing beyond reproducing themselves.

An example of a virus which is not a malware, but is putatively benevolent, is Fred Cohen's compression virus. However, antivirus professionals do not accept the concept of benevolent viruses, as any desired function can be implemented without involving a virus (automatic compression, for instance, is available under the Windows operating system at the choice of the user). Any virus will by definition make unauthorised changes to a computer, which is undesirable even if no damage is done or intended. On page one of Dr Solomon's Virus Encyclopaedia, the undesirability of viruses, even those that do nothing but reproduce, is thoroughly explained.

Amelanchier

Amelanchier (pronounced /æməˈlænʃɪər/ am-ə-lan-sheer), also known as shadbush, shadwood or shadblow, serviceberry or sarvisberry, juneberry, saskatoon, sugarplum or wild-plum, and chuckley pear is a genus of about 20 species of deciduous-leaved shrubs and small trees in the Rose family (Rosaceae).

Amelanchier is native to temperate regions of the Northern Hemisphere, growing primarily in early successional habitats. It is most diverse taxonomically in North America, especially in the northeastern United States and adjacent southeastern Canada, and at least one species is native to every U.S. state except Hawaii and to every Canadian province and territory. Two species also occur in Asia, and one in Europe. The taxonomic classification of shadbushes has long perplexed botanists, horticulturalists, and others, as suggested by the range in number of species recognized in the genus, from 6 to 33, in two recent publications. A major source of complexity comes from the occurrence of hybridization, polyploidy, and apomixis (asexual seed production), making species difficult to characterize and identify.

The various species of Amelanchier grow to 0.2–20 m tall; some are small trees, some are multistemmed, clump-forming shrubs, and yet others form extensive low shrubby patches (clones). The bark is gray or less often brown, and in tree species smooth or fissuring when older. The leaves are deciduous, cauline, alternate, simple, lanceolate to elliptic to orbiculate, 0.5–10 x 0.5–5.5 cm, thin to coriaceous, with surfaces above glabrous or densely tomentose at flowering, and glabrous or more or less hairy beneath at maturity.

The inflorescences are terminal, with 1–20 flowers, erect or drooping, either in clusters of one to four flowers, or in racemes with 4–20 flowers. The flowers have five white (rarely somewhat pink, yellow, or streaked with red), linear to orbiculate petals, 2.6–25 mm long, with the petals in one species (A. nantucketensis) often andropetalous (bearing apical microsporangia adaxially). The flowers appear in early spring, "when the shad run" according to tradition (leading to names such as "shadbush"). The fruit is a berry-like pome, red to purple to nearly black at maturity, 5–15 mm diameter, insipid to delectably sweet, maturing in summer.