A virus, which infects the original boot sector on a floppy diskette. These viruses are particularly serious because information in the boot sector is loaded into memory first, before virus protection code can be executed. A "strict" boot sector infector infects only the boot sector, regardless of whether the target is a hard disk or a floppy diskette. Some viruses always attack the first physical sector of the disk, regardless of the disk type.
A boot sector infector virus places its starting code in the boot sector. When the computer tries to read and execute the program in the boot sector, the virus goes into memory where it can gain control over basic computer operations. From memory, a boot sector infector can spread to other drives (floppy, network, etc.) on the system. Once the virus is running, it usually executes the normal boot program, which it stores elsewhere on the disk. Also: Boot Virus, Boot Sector Virus, BSI.