In medicine, a very simple microorganism that infects cells and may cause disease. Because viruses can multiply only inside infected cells, they are not considered to be alive.
A program that attaches itself to an executable file or vulnerable application and delivers a payload that ranges from annoying to extremely destructive. A file virus executes when an infected file is accessed. A macro virus infects the executable code embedded in Microsoft Office programs that allows users to generate macros.
A computer program file capable of attaching to disks or other files and replicating itself repeatedly, typically without user knowledge or permission. Some viruses attach to files so when the infected file executes, the virus also executes. Other viruses sit in a computer's memory and infect files as the computer opens, modifies, or creates the files. Some viruses display symptoms, and others damage files and computer systems, but neither is essential in the definition of a virus.
A computer program that can replicate itself, infect a computer without permission or knowledge of the user, and then spread or propagate to another computer.
A microscopic infectious organism that reproduces inside living cells.