The Wii U GamePad is relatively easy to reverse-engineer, said one of the people who did it, in an interview with Eurogamer.
Pierre Bourdon, who worked on the GameCube and Wii emulator known as Dolphin, told Eurogamer that the GamePad is "actually not a very secure device (compared to the Wii U)" when it comes to its communication with the system. Because the GamePad's firmware is held in unencrypted flash storage, Bourdon and his cohorts were able to reverse-engineer the code "pretty easily."
They discovered that the GamePad's wireless connection is almost standard 802.11n Wi-Fi, which made it possible for them to pair the controller with a PC within less than a week. Unlike the Wii Remote, which uses Bluetooth, controller inputs from the GamePad are transmitted over the same Wi-Fi connection.
That means that there's a slight possibility that the Wii U could eventually be upgraded to send video and audio to the internet as well as the GamePad, although doing both at the same time would be difficult, according to Bourdon.