It seems that in the 24th Chaos Communication Congress (the 24C3, an annual German-based hacking meeting) a hacking group has shown how they have fully hacked the Wii. There is also a video of it and here a new from nintendo-scene.com summarizing the event.

Until now games for Wii could be already played without being the original, and Wii was already hacked in the GameCube mode. The achievement of this group is that, now, it is fully accessible in Wii mode, which means that, future homebrew software is going to be able to control all of the hardware inside the Wii, as happens with other consoles like the DS.