I am a Minecraft modder, and I have a youtube channel teaching other people how to make mods for Minecraft (www.youtube.com/henrythecoder). Recently, youtube has offered me to participate in "revenue sharing", where basically youtube puts ads on my videos, and in turn I get paid a small amount of money per view. However, in order for me to qualify for this, I have to certify that I own the rights to everything I do in the video, and that what I am doing is legal. Thus, I need to find out if it is actually legal to make mods for Minecraft.
For those of you who may not know Minecraft very well, it's a game with a very large modding community. I don't know if the makers of Minecraft "officially" support people making mods (Minecraft isn't open source), but they certainly make no effort whatsoever to stop it. In the next update of Minecraft, the makers of the game have also revealed that the game may include built in mod support (making it easier to install mods).