I know there have to be some gamers amongst us. Here is a topic that tackles an interesting legal battle. I will link a few passages at the end of this explanation which sheds greater detail on the nature of the legal debate.
Blizzard Entertainment has always been very interactive with its community. With the release of Starcraft, they also included a extremely intuitive map editor which all members of the community could use. There was mixed success in the endeavors that programmers and enthusiasts took in creating these map mods. It was not until the release of Warcraft 3: Reign of Chaos and the expansion The Frozen throne that these map modifications took on a whole new life of their own. With the help of others, a programmer dubbed Icefrog created one of the first MOBA games (trolls will say that the SC1 map AoS, or Aeon of Strife was the original genre), Defense of the Ancients (Or DotA). This map became a huge success and even spawned worldwide invitationals. Another gaming powerhouse, Valve, later hired Icefrog to oversee a ‘sequel’ to DotA, aptly named Dota 2. In the creation of this game, Valve took legal action to trademark ‘DotA’, ‘Defense of the Ancients,’ etc. The end-user agreement for Warcraft III stated that no one could profit from any map editor creations. They, however, did not follow their own guidelines as a company, by holding profitable tournaments surrounding a mod they did not own. Does Blizzard have more of a claim than Valve to this trademark though? Here is the more important question:
Should a mod that a user creates be owned by the original game developer?