a virus is a self-replicating
...itself into other executable code or documents (for a complete definition: see below). Thus, a computer virus behaves in a way similar to a biological virusList of biological viruses A virus is a small particle which can infect other biological organisms. Viruses are obligate intracellular parasites meaning that they can only reproduce by invading and taking over other cells as they lack the cellular machinery for self reproduction. The term virus usually refers to those particles which infect eukaryotes (multi-celled organisms and many single-celled organisms), whilst the term bacteriophage or phage is used to describe those infecting prokaryotes (bacteria an... [click for more], which spreads by inserting itself into living cells. Extending the analogy, the insertion of the virus into a program is termed infection, and the infected file (or executable code that is not part of a file) is called a host. Viruses are one of the several types of malwareMalware (a portmanteau of "malicious software") is any software developed for the purpose of doing harm to a computer system. Malware can be classified based on how it is executed, how it spreads, and/or what it does. The classification is not perfect, however, in the sense that the groups often overlap and the difference is not always obvious, giving rise to frequent flame wars.... [click for more] or malicious software. In common parlance, the term virus is often extended to refer to computer wormsA computer worm is a self-replicating computer program, similar to a computer virus. A virus attaches itself to, and becomes pa...