The J&M virus is a slightly complex virus which infects the master boot records of hard disks and the floppy boot sector. Besides having a destructive payload routine, this virus uses encryption in an attempt to hide it's own virus code.

Upon activation of the payload on November 15th , the virus enters an infinite loop and formats the first track of the first hard drive.

On hard disks this virus stores a copy of the original master boot record at physical location cylinder 0 side 0 sector 6. On floppy disks the original boot sector is stored at physical location cylinder 0 side 1 sector 14.