I wanted to learn more about what a computer virus was and how to deal with them. It turned out that a computer virus is a program without the user being introduced into computers and there are various manufactures unauthorized actions. Computer viruses have the ability to reproduce. The ability of viruses to multiply causes some people want to compare them with a special form of life and even endow these programs by some evil intelligence. However, this is nothing more than fiction and fantasy game. Computer viruses are one of the subtypes of a large class of programs called malware. Today these concepts are often identified, however, from a scientific point of view, this is not true. The so-called worms and Trojan horses are among the most popular types of virus. Their main difference is that they cannot reproduce. The program - worm spreads over computer networks (local or global), without resorting to replication. Instead it automatically sends its original, for example, by e-mail without the user knowing. Trojans are generally devoid of any built-in features of distribution: they get on the computers solely with their authors or persons who illegally use them. For example, users have an email with a proposal to send files to run. After you run this file to your computer, it invisibly enters the program, perform various unwanted actions. There are various methods of combating viruses.