Bannerbomb is a Wii exploit capable of launching homebrew from the System Menu version 4.2 or below. It was created by Comex to replace the Twilight Hack, which hasn't worked since System Menu 4.0.
NOTE: The original Bannerbomb exploit does not work with System Menu 4.2, it only works with System Menu 4.1 or older. However Bannerbomb v2 has been released by Comex, and works on 4.2. No version of Bannerbomb works on System Menu 4.3 or newer; use LetterBomb, Smash Stack, Indiana Pwns, Bathaxx or Return of the Jodi instead.
The exploit works by using a malformed banner to crash the Wii and run code to load the boot.dol placed in the root of the SD card. It can be used to install the Homebrew Channel, DVDx and the BootMii public beta via the HackMii Installer.
There is an ongoing effort to discover the results of installing the Bannerbomb channel onto the Wii's NAND.