Bannerbomb is an exploit capable of launching homebrew from any version of the System Menu. It was created to replace the Twilight Hack, which does not work on System Menu 4.0.
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.