boot virus An {MS-DOS} {virus} that infects the {boot record} program on {hard disk}s and {floppy disk}s or the {master boot record} on hard disks. The virus gets loaded into memory before {MS-DOS} and takes control of the computer, infecting any floppy disks subsequently accessed. An infected {boot disk} may stop the computer starting up at all. (1995-02-16)