[almost certainly from Elmer Fudd's immortal line “You wascawwy wabbit!”]
1. A legendary early hack reported on a System/360 at RPI and elsewhere around 1978; this may have descended (if only by inspiration) from a hack called RABBITS reported from 1969 on a Burroughs 5500 at the University of Washington Computer Center. The program would make two copies of itself every time it was run, eventually crashing the system.
2. By extension, any hack that includes infinite self-replication but is not a virus or worm. See fork bomb and rabbit job, see also cookie monster.