Apparently it's possible to play all of Mario Kart DS's thirty-two tracks online, even though you're not supposed to...

For technical reasons no one is quite sure of, only two thirds of the tracks in Mario Kart DS can be played online via the Wi-Fi Connection. Some fans were dissapointed at this, especially as some of the game's most popular tracks - namely Waluigi Pinball, Tick Tock Clock and Airship Fortress - were some of the courses which could only be played via LAN.

However, a gamer going under the alias of 'Parasyte' has apparently cracked the game. He doesn't go into details of how he has achieved this, but as the missing track data is on every cartridge it is presumably not that hard to trick the DS into letting the remainder of the tracks be played online too.

The 'hidden' tracks are apparently not flawless when played online, with several glitches appearing. It still begs the question though, why these tracks were chosen to be ommitted by Nintendo in the first place.