Computer virus

A computer virus is a computer program that can copy itself and infect a computer without the permission or knowledge of the owner. The term "virus" is also commonly but erroneously used to refer to other types of malware, adware, and spyware programs that do not have the reproductive ability. A true virus can only spread from one computer to another (in some form of executable code) when its host is taken to the target computer; for instance because a user sent it over a network or the Internet, or carried it on a removable medium such as a floppy disk, CD, DVD, or USB drive. Viruses can increase their chances of spreading to other computers by infecting files on a network file system or a file system that is accessed by another computer.^[1][2]

The term "computer virus" is sometimes used as a catch-all phrase to include all types of malware. Malware includes computer viruses, worms, trojan horses, most rootkits, spyware, dishonest adware, crime ware, and other malicious and unwanted software), including true viruses. Viruses are sometimes confused with computer worms and Trojan horses, which are technically different. A worm can exploit security vulnerabilities to spread itself to other computers without needing to be transferred as part of a host, and a Trojan horse is a program that appears harmless but has a hidden agenda. Worms and Trojans, like viruses, may cause harm to either a computer system's hosted data, functional performance, or networking throughput, when they are executed. Some viruses and other malware have symptoms noticeable to the computer user, but many are surreptitious.

Most personal computers are now connected to the Internet and to local area networks, facilitating the spread of malicious code. Today's viruses may also take advantage of network services such as the World Wide Web, e-mail, Instant Messaging, and file sharing systems to spread.

TEXT #19

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Virus

A virus (from the Latin virus meaning toxin or poison) is a sub-microscopic infectious agent that is unable to grow or reproduce outside a host cell. Viruses infect all types of cellular life. The first known virus, tobacco mosaic virus, was discovered by Martinus Beijerinck in 1898, and now more than 5,000 types of virus have been described in detail, although most types of virus remain undiscovered. Viruses infect all forms of life, are found in almost every ecosystem on Earth, and are the most abundant type of biological entity on the planet.

Viruses consist of two or three parts: all viruses have genes made from either DNA or RNA, long molecules that carry genetic information; all have a protein coat that protects these genes; and some have an envelope of fat that surrounds them when they are outside a cell. Viruses vary in shape from simple helical shapes to more complex structures. They are about 1/100th the size of bacteria. The origins of viruses are unclear: some may have evolved from plasmids—pieces of DNA that can move between cells—others may have evolved from bacteria. In evolution, viruses are an important means of horizontal gene transfer.

Viruses spread in many ways; plant viruses are often transmitted from plant to plant by insects that feed on sap, such as aphids, while animal viruses can be carried by blood-sucking insects. These disease-bearing organisms are known as vectors. Influenza viruses are spread by coughing and sneezing, and others such as norovirus, are transmitted by the faecal-oral route, when they contaminate hands, food or water. Rotaviruses are often spread by direct contact with infected children. HIV is one of several viruses that are transmitted through sex.

Not all viruses cause disease, as many viruses reproduce without causing any obvious harm to the infected organism. Some viruses such as hepatitis B can cause life-long or chronic infections, and the viruses continue to replicate in the body despite the hosts' defense mechanisms. However, viral infections in animals usually cause an immune response, which can completely eliminate a virus. Microorganisms such as bacteria also have defenses against viral infection, such as restriction modification systems. Antibiotics have no effect on viruses, but antiviral drugs have been developed to treat life-threatening and more minor infections.

TEXT #20

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In search of the perfect home

For John Mew and his wife Josephine their home really is their castle. They have built their own English castle in the Sussex countryside. The building is brand new with all the luxuries you would expect from a house that cost more than 350,000$ to build. However, when you first see it from the outside it would be easy to think that you are looking at an ancient monument. The building has a lot of the features of a traditional castle, including a keep, a moat and a drawbridge. “My choice of house is somewhat eccentric and building it was very hard work, but we’ve got the perfect place to live” Mew says. Although some would say that the building is impractical and may be cold in harsh British winters, he certainly has got a unique and spacious home.

Dan Garner, a tree surgeon from Gloucestershire, certainly thinks that this is the way to go up in the world. “When our family became short of space at home our solution was to built into a spruce tree six metres above the ground. It has one main room, a bedroom and a balcony running around two sides”. Garner is so happy with this practical extension to his home that he thinks he can convince more people of the benefits of living in the trees. He wants to set up his own enterprise making more of the deluxe tree dwelling, saying “Tree houses are airy, secure and comfortable and the only disadvantage is that they might not be suitable for people who suffer from hay fever or a fear of heights!”

Even people who live in more ordinary settings sometimes can’t resist doing something to make them stand out from the crowd. One extreme example of this is Bill Heines’s house in Headington, Oxfordshire. Until one morning in 1986, his house looked much like all the others in his street, when suddenly overnight a 7.5 m long firbeglass shark appeared to have crashed through the roof. The shark was sculpture by local artist John Buckley. At first some people complained that it might be dangerous or that it spoilt the look of the neighbourhood, but engineers checked that the sculpture was safe and ‘Headington shark’ has become a well-known and popular landmark. It seems that no matter where you live, you can always do something to make sure your house says something about who you are.

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