Blizzard has appealed Valve’s attempt to trademark "Defense of the Ancients" (DOTA) in the lead up to the latter’s release of DOTA 2.

DOTA is a highly popular mod of Blizzard’s Warcraft III. Valve hired the longest-serving designer of the mod, “IceFrog”, to create a fully-fledged sequel for release on its digital distribution platform, Steam.

However, Blizzard is also developing an action real-time strategy game it calls Blizzard DOTA. Valve’s move to trademark DOTA would expose Blizzard to litigation should it attempt to use the term for its own official take on the Warcraft III mod.

In a Notice of Opposition to the United States Trademark and Patent office, Blizzard writes, “Blizzard Entertainment … believes that it will be damaged by the registration of the mark … and hereby opposes its registration.”

Blizzard argues that “for more than seven years” DOTA has been “used exclusively by Blizzard and its fan community, under license from Blizzard.” It argues that DOTA is built on the Warcraft III engine and “utilises the game’s interface, and gameplay mechanics; that is comprised of Warcraft III characters, items, spells, artwork, textures, and color palates; that can be played only using Warcraft III software and via Blizzard's online service; and whose name (DOTA, an acronym for ‘Defense of the Ancients’) is a reference to Warcraft III characters known as the ‘Ancients.’”

Blizzard goes on: “In contrast to Blizzard … Valve … has never used the mark DOTA in connection with any product or service that currently is available to the public. By attempting to register the mark DOTA, Valve seeks to appropriate the more than seven years of goodwill that Blizzard has developed in the mark DOTA and in its Warcraft III computer game and take for itself a name that has come to signify the product of years of time and energy expended by Blizzard and by fans of Warcraft.”

“Valve has no right to the registration it seeks,” states Blizzard. “If such registration is issued, it not only will damage Blizzard, but also the legions of Blizzard fans that have worked for years with Blizzard and its products, including by causing consumers to falsely believe that Valve's products are affiliated, sponsored or endorsed by Blizzard and are related or connected to Warcraft III.”

There are no firm release dates for either Valve’s DOTA 2 or Blizzard DOTA.