There is only one file type that uses the .WII extension:
Scrambled Wii Disc Image
Disc image format used by the homebrew community for Nintendo Wii discs; saves a Wii game in a scrambled format; can be unscrambled and converted to the .ISO format with Wii Unscrambler and then burned to a standard disc; sometimes used for backing up Wii games.
The WII format is not supported by Nintendo, the developers of the Wii game console system.
Updated: June 25, 2012