While there are many people that couldn't wait to get their new Nintendo Wii U home and play the latest games, some people had a different idea. Just like any other console or bit of technology before it, hackers couldn't wait to tear the Wii U a digital new one. Piracy is a big issues for all games consoles and while this latest hack isn't exactly "piracy" it is the first step towards opening up the console for other non standard uses, including back-up games.
The new hack only works in the original Wii mode (a build in Wii emulator), no the Wii U mode. By adding the Homebrew channel it allows the installation of user created code that is often used to play things like emulators or homebrew games.
Nintendo isn't going to take this intrusion lying down though and has already stated that if you install this mod, you can kiss your warranty goodbye, not only that but Nintendo has said they are willing to repel hacking attempts, likely with firmware updates that will either close the loop hole or block features on hacked consoles.