Super Smash Bros. Online
From Mario Fan Games Galaxy Wiki
Super Smash Bros. Online was a fangame hoax.
The Program
Running the program yielded a green ball with white balls on top of it -- possibly some variant of a face contortion -- and a loud, badly compressed screaming WAV. This WAV was later sent around AIM to those suspecting or off-guard alike until everybody was sick of it and all copies of the WAV were deleted.