What is a Boot Sector Virus?
A boot sector virus is a computer virus which infects the boot sector on hard disks, floppy disks, and theoretically also other bootable media such as CD's and DVD's.
A boot sector virus does not need to be able to successfully boot the victims computer to infect it. Because of this, even non-bootable media can spread a boot sector virus.
Once the infected computer successfully boots, the boot sector virus stays in memory and infects floppies and other media when they are written to by the infected computer.
Boot sector viruses have become increasingly less common as floppy disks have become rarer.