Hard disk drives, floppy diskettes, and logical drives (partitions) all have boot sectors where critical drive information is stored. See also partition table, Master Boot Record, and multi-partite viruses.

Boot Sector or MBR Virus - A virus which infects the boot sector of a fixed or floppy disk. Any formatted disk (even one that is blank, or only contains text data, for example) may contain a boot sector virus. An attempt to boot from a diskette infected with a boot sector virus will cause the virus to become active in memory. This type of virus will place a copy of itself on the Master Boot Record (MBR) or the boot sector of the hard drive. Every time you boot your system from that point on, you will have the virus active in memory. These are the most common viruses. Any attempt to disinfect these viruses while a virus is active in memory will be defeated since it will re-write itself to the disk as soon as you remove it. Additionally, many of these are stealth viruses. For safety's sake, you should always attempt to disinfect these viruses after a cold boot to a write-protected diskette.

Updated On: 04.03.28