Program that infects other files
The term 'computer virus' is often used as a general term for all types of malware, including trojans and other non-replicating malicious code. In a stricter sense 'virus' applies only to self-replicating malware, and even more specifically only to code which infects other files on the local system (rather than spreading from one system to another in the form of an unchanging file, as is the case with most worms).
The first use of the term 'computer virus' is attributed to Fred Cohen who used it in 1983 during a seminar on computer safety at Lehigh University. He used the term on the recommendation of his advisor, Prof. Leonard Adleman who, it is claimed, picked the name from science fiction novels. Fred Cohen's original definition of a computer virus as of 1983 was: `a program that can "infect" other programs by modifying them to include a possibly evolved copy of itself'. He updated the definition a year later in 1984 in his paper entitled `Computer viruses - theories and experiments'.