A computer virus is a computer program that can copy itself and infect a computer without permission or knowledge of the user. The original may modify the copies or the copies may modify themselves, as occurs in a metamorphic virus. A virus can only spread from one computer to another when its host is taken to the uninfected computer, for instance by a user sending it over a network or carrying it on a removable medium such as a floppy disk, CD, USB drive or by the Internet. Additionally, viruses can spread to other computers by infecting files on a network file system or a file system that is accessed by another computer. Viruses are sometimes confused with computer worms and Trojan Worms. A worm can spread itself to other computers without needing to be transferred as part of a host, and a Trojan Worm is a file that appears harmless until executed.
Many 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, and file sharing systems to spread, blurring the line between viruses and worms. Furthermore, some sources use an alternative terminology in which a virus is any form of self replicating malware.
Some viruses are programmed to damage the computer by damaging programs, deleting files, or reformatting the hard disk. Others are not designed to do any damage, but simply replicate themselves and perhaps make their presence known by presenting text, video, or audio messages. Even these benign viruses can create problems for the computer user. They typically take up computer memory used by legitimate programs. As a result, they often cause erratic behavior and can result in system crashes. In addition, many viruses are bug-ridden, and these bugs may lead to system crashes and data loss.
A computer virus can do extensive damage. It can crash your hard disk. It can destroy all or some of your data. Many viruses do weird little things that adversely affect your computer. The most usual symptom of a computer virus is erratic behavior. The destruction can happen at any rate of speed and can affect almost any part of the computer. Viruses can spread quickly through today's intricate cyber world. If your computer starts to act a little weird, the first thing to do is to check for a virus.
If you are smart, you will stop viruses before they enter your computer. You can do this by purchasing a good virus protection program. Such a program will check all files for viruses. Once installed, an antivirus program can be set to work in the background. It will check all files before they enter your computer and will alert you if a virus is detected before it contaminates your system. If a virus is detected, your antivirus program will quarantine or eliminate it so that it cannot harm your computer.
Be very careful to purchase a virus protection program that matches your operating system. If you use a Mac, buy a virus protection program made especially for Macintosh computers. If you use Windows 98 or Me or XP, select a program that was written specifically for your operating system. Don't try to use a virus protection program that was written for Windows 95 on a Windows XP machine; this will really mess up your computer.