What is a computer virus?
It is an executable code able to reproduce itself. Viruses are an area of pure programming, and, unlike other computer programs, carry intellectual functions on protection from being found and destroyed.
Yes, viruses seem to be the only alive organisms in the computer environment, and yet another their main goal is survival. That is why they may have complex crypting/decrypting engines, which is indeed a sort of a standard for computer viruses nowadays, in order to carry out processes of duplicating, adaptation and disguise.
It is necessary to differentiate between reproducing programs and Trojan horses. Reproducing programs will not necessarily harm your system because they are aimed at producing as many copies of their own as possible by means of so-called agent programs or without their help.
Meanwhile Trojan horses are programs aimed at causing harm or damage to PC's.
Destructive actions are not an integral part of the virus by default. However virus-writers allow presence of destructive mechanisms as an active protection from finding and destroying their creatures, as well as a response to the attitude of society to viruses and their authors.
As you see, there are different types of viruses, and they have already been separated into classes and categories. For instance: dangerous, harmless, and very dangerous.
But viruses are famous not only for their destructive actions, but also for their special effects, which are almost impossible to classify. But one should remember that special effects must occur only after a certain number of contaminations. Users should also be given a chance to restrict execution of destructive actions, such as deleting files, formatting hard disks. Thereby a virus can be considered to be a useful program, keeping a check on system changes and preventing any surprises such as deletion of files or wiping out hard disks.
It sounds quite unusual to say such words about viruses, which are usually considered to be a disaster. The less a person understands in programming and virology, the greater influence will have on him the possibility of being infected with a virus. Thus, let's consider creators of viruses as the best source.



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Until the late 1970s, the computer was viewed as a massive machine, most people were intimidated by them. As technology advanced, this was changed by a group of engineers and entrepreneurs who rushed to improve the designs of then current technology and to make computers easier to use. This was a very competitive and stressful time, and the only people who succeeded were the ones who were very
resourceful.
Much of this activity was centered in the Silicon Valley in north¬ern California. Between 1981 and 1986, more than 1000 new technology-oriented businesses started there.
Robert Noyce was a risk-taker who was successful both as an engi¬neer and as an entrepreneur. A graduate of the Massachusetts Institute of Technology (MIT), he started working for one of the first computer-related businesses in 1955.As an engineer, he co-invented the integrated circuit, which was the basis for later computer design. This integrated circuit was less than an eighth of an inch square but had the same power as a transistor unit that was over 15 inches square or a vacuum tube unit that was 6.5 feet square. As a businessman, Noyce co-founded Intel, one of the most successful companies in the Silicon Valley and the first company to introduce the microprocessor.
The two men who first introduced the personal computer (PC) to the marketplace had backgrounds unlike Robert Noyce's. Twenty-year-old Steven Jobs and twenty-four-year-old Stephen Wozniak were college drop-outs who had collaborated on their first project as computer hobbiests in a local computer club. Their first personal computer utilized the technology of Noyce's integrated circuit. It was typewriter-sized, as powerful as a much larger computer, and inexpensive to build. Wozniak designed the first model, and Jobs devised its applications and attracted interest from investors and buyers. Jobs insisted that the computers be light, trim, and made in muted colors. These features helped convince a skeptical public that the computer was practical for the home and small business.
As the computer industry began to reach into homes and small businesses around the world, the need for many new products for the personal computer began to emerge. Martin Alpert, the founder of Tecmar, Inc., was one of the first people to foresee this need. He designed memory extenders that enabled the comput¬er to store more information, and insertable boards that allowed people to use different keyboards while sharing the same printer. Alpert had neither the technical training of Noyce nor the com¬puter clubs of Jobs and Wozniak to encourage his interest in com¬puter engineering. His wife recognized the potential of his projects before he did, and enrolled in a graduate program in business manage¬ment so she could run his electronics business successfully.
Computer technology has opened a variety of opportunities for people who are creative risk-takers. They have known when to use the help of other people and when to work alone. Rarely in history have so many people been so motivated to create. Many of them have been rewarded greatly with fame and fortune, and the world has benefited from this frenzy of innovation.