The term computer viruses has entered into popular demonology. The essence of a computer virus is that, like its human equivalent, it may be transmitted from one computer to another. This may occur when an infected disk is transferred between computers. In the event that computers are linked together either in a network or using a telecommunications connection, the virus may also be transmitted electronically. Having infected a computer, the effects of viruses may vary widely.
Some viruses are relatively benign.
In one of the most notorious instances reported from the United States, a student at Cornell University wrote a computer program referred to as a worm. A worm is a program which replicates itself. Although initially, it may produce few adverse effects, the continuing doubling in size begins to consume larger and larger amounts of the computer system's memory. Ultimately, it will consume the storage space available and, by overwriting material which is already there, will cause the loss of that data. In the case in question, the worm was let loose on the Internet .