Overview
The Wii is designed to prevent the use of unauthorized software and Nintendo actively attempts to prevent the use of Homebrew Channel with each of its software updates for the Wii. As a result, installation of the Homebrew Channel requires the use of various software exploits and workarounds.
Earliest attempts used a bug present in System Menu 3.2 and below in the signature verification of discs in conjunction with a modchip. In systems using software prior to System Menu 4.0, users could load an exploit in the Wii version of The Legend of Zelda: Twilight Princess, and a specially crafted game save called the Twilight Hack copied from an SD card. As of the System Menu 4.0 update, the Twilight Hack had been entirely disabled.
In response to the System menu 4.0 update, Bannerbomb, which uses an exploit in the Wii System Menu (so therefore only requires a normal sized SD card), was developed. Bannerbomb is a software exploit that exploits a bug in the way the Wii renders channel banners. The original version of Bannerbomb was disabled in System Menu 4.2. A further exploit was later discovered and is exploited in the "SD Card Menu". System Menu 4.3 has disabled the Bannerbomb exploit used to load unauthorized software.
In systems using System Menu 4.2 or 4.3, users could exploit a buffer overflow in Lego Indiana Jones: The Original Adventures and use the "HackMii" installer that is loaded on an SD card. The specially-crafted save that uses this exploit to run code is called "Indiana Pwns". Users could also exploit a flaw in custom stage loading in an NTSC version of Super Smash Bros. Brawl to run an installer such as HackMii. The specially-crafted stage that uses this exploit to run code is called "Smash Stack", and is a particularly reliable way of loading homebrew because the game can load custom stages directly from the SD, completely bypassing the System Menu; Nintendo cannot easily fix bugs on game discs, making this exploit particularly difficult to disable. An exploit for LEGO Star Wars: The Complete Saga called "Return of the Jodi" also exists and can run the "HackMii" Installer. "Letterbomb" can be used like "Bannerbomb" to install hackmii and the Homebrew channel.
Users who had already installed the Homebrew Channel prior to updating their Wiis to System 4.2 or 4.3 could allow the Homebrew Channel to self update which had already been updated to a version that circumvented the System 4.2 and 4.3 prevention measures. There are unofficial download sites that also provide this workaround.
Later, a hack was released and is called Yu-Gi-OWNED, and it works on any system menu. This exploit is based on the Indiana Pwns exploit, and the Twilight Hack. This exploit runs on PAL Wiis, while a separate exploit called "Yu-Gi-VAH" can be used on NTSC consoles. SDHC are not currently working with this exploit, so a normal SD card is required. On August 9th, 2011 Team Twiizers released a new exploit named LetterBomb which exploits a bug used in the Wii's internal messaging system that works with System Menu 4.3. After that, Team Twiizers released another exploit called "Bathaxx". This took advantage of another loading issue in the game LEGO Batman. It works on System Menu 4.3.
"Letterbomb" was released for all system menu versions in August 2011. Unlike other exploits, it does not require a trigger disc.
Read more about this topic: Homebrew Channel