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. It can spread from one computer to another by help of network connection or carrying it on a removable medium such as floppy disk, CD, DVD, USB drive or by the Internet. But viruses are not equal to computer worms and Trojan horses. A worm can spread itself to other computers without being transferred as a part of a host, and a Trojan horse is a file that appears harmless until executed.
Many PCs are now connected to the Internet and/or to local area networks. Today's viruses may also take advantage of network services (World Wide Web, e-mail, file sharing systems). Some viruses are programmed to damage the computer by damaging programs, deleting files, or reformatting the hard disk. Others are harmless, but simply replicate themselves and make their presence known by presenting text, video, or audio messages. Although these viruses are not dangerous, they can create problems for the computer user. 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.
Many PCs are now connected to the Internet and/or to local area networks. Today's viruses may also take advantage of network services (World Wide Web, e-mail, file sharing systems). Some viruses are programmed to damage the computer by damaging programs, deleting files, or reformatting the hard disk. Others are harmless, but simply replicate themselves and make their presence known by presenting text, video, or audio messages. Although these viruses are not dangerous, they can create problems for the computer user. 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.
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