As influential as Warcraft III was in the real-time strategy genre, the game's most enduring legacy might be as the basis for genre-defining, fan-made custom game spin-offs like Defense of the Ancients (aka Dota) and Auto Chess in its wake. Now, Blizzard is taking steps to ensure it retains complete ownership of any such custom games that originate from its titles in the future, including those that come out of Warcraft III's recently released Reforged update

As noted by PC Gamer, a recent update to Blizzard's Acceptable Use Policy expands the legal rights that custom-game makers automatically assign to Blizzard (new language highlighted in bold; old language available on The Internet Archive).

Custom Games are and shall remain the sole and exclusive property of Blizzard. Without limiting the foregoing, you hereby assign to Blizzard all of your rights, title, and interest in and to all Custom Games, including but not limited to any copyrights in the content of any Custom Games.

Blizzard's claim on custom-game copyrights is important because while it's hard to effectively copyright the basic concept of a game , you can copyright the original characters, art, and writing associated with the game itself. Blizzard learned this the hard way a decade ago, when Valve bought the Dota copyright from some of the modders who created it.

After Valve's rights were confirmed in a 2012 out-of-court settlement, Valve was able to turn around and create Dota 2. Blizzard, meanwhile, had to settle for creating the Dota-style Heroes of the Storm with its own characters.

A similar process repeated itself last year with Auto Chess, a popular mod built on top of Valve's Dota 2. While the general autobattler concept has become popular enough to become a genre in its own right, Valve's terms of service never claimed ownership of the copyright for Dota 2's derivative works. Thus, the name Auto Chess still belongs to developer Drodo Studio, which used it to create a standalone version of the game for the Epic Games Store.

Under Blizzard's new legal language, any similar games created from the base of Reforged would be completely controlled by Blizzard. While other developers would be able to copy the general gameplay for their own purposes, any derivative games that use the same name, art, or characters would belong to Blizzard.

While Blizzard doesn't allow custom-game developers to engage in direct "commercial exploitation" from their creations, those developers are allowed to accept donations to recoup the "time and resources" involved in creating the game (with some restrictions). Blizzard also retains the right to "remove Custom Games from its systems and/or require that a Custom Game developer cease any and/or all development and distribution of a Custom Game."

These more restrictive policies probably won't have a direct effect on the vast majority of Warcraft modders, who create custom content for fun more than for profit. But if another mod of a Blizzard game becomes a hot new trend in the gaming world, this new language could ensure that the resulting profits go to Blizzard and not the modders themselves.

We're currently examining all the other changes made in Warcraft III: Reforged (for better and worse) and should have a report in the coming days.