virus

　Second, about the computer virus. A virus is a computer program that infects programs with copies of itself. It clones itself from disk to disk or from one system to another over computer networks. Besides viruses, there are dangerous programs which are not viruses. These include worms, Trojan horses, and logic bombs. The damage caused by viruses may be harmless, such as displaying a happy birthday message for the creator on his birthday. But the virus may do considerable damage. For example, destroying important records, file tables, and valuable data on disk. To protect our programs, we must back up constantly, prepare security system, and we should know viruses. Most of the web sites have extensive information on viruses, including databases, recent activities, and even virus hoaxes.