Bootvirus
A bootvirus is a small program which copies itself unauthorized to the bootblock of unprotected floppy disks. The bootblock of a floppy disk contains 1024 byte of programcode. This code is the first thing the AmigaDOS executes if you put in a floppy disk.
The bootblock uses diskblock 0 and 1 of a floppy disk (one block = 512 byte)