Baboon is a boot sector virus with some special functions in it.
It infects the boot sector of floppy disks and MBRs (Master Boot Record) of hard disks. Baboon does not save the original boot sector or MBR anywhere. The virus searches for the active boot sector in the MBR data area, reads the active boot sector and gives control to it. Thus it keeps the general functionality of the MBR code.
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
When the PC is booting from an infected floppy, the virus will also read the active boot sector from the hard drive and give control to it. No error message like "non-system disk" will be displayed and the PC will boot directly from the hard disk.
Baboon activates both randomly and on the 11th of September. At this time it overwrites the MBR of the hard drive and the first 9 sectors of the active partition. As a result the PC will not boot.
Baboon was reported to be in the wild in September 1997, but does not seem to be really common.
Technical Details: Peter Szor, F-Secure, 1997