Yes, this came out on April 1st.... But, it does appear that enough folks have been loading and running, that it is probably not a joke. Using Magic Latern, folks have loaded a bootloader, that in turn loads and runs a Linux distribution (for an ARM processor) on the co-processor within a Canon body (off the SD card). That is the reason that it works on Canon and will not work on any other body - as none of the others have a dual processor architecture.
.... which means that virus, trojans, hacks, root kits etc. will soon follow, providing yet another avenue for system infections.