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Following the discovery of a buffer overflow vulnerability in the Wii version of Twilight Princess, an exploit known as the "Twilight Hack" was developed, allowing the execution of custom code from a Secure Digital (SD) card on the console. A properly designed save file would cause the game to load unsigned code, which could include Executable and Linkable Format (ELF) programs and homebrew Wii applications. Versions 3.3 and 3.4 of the Wii Menu prevented copying exploited save files onto the console until circumvention methods were discovered, and version 4.0 of the Wii Menu patched the vulnerability.

What does ELF stand for?
Executable and Linkable Format