Blizzard has won the first round of a legal battle against the maker of software that automates game play in World of Warcraft.
It brought the case against MDY Industries claiming its WowGlider program infringed its copyright.
An Arizona district court has ruled MDY does infringe Blizzard's copyright but not in the way the game maker claimed.
WowGlider controls characters in Warcraft so they kill enemies and loot them automatically.
The summary judgement by US District Court Judge David Campbell says that MMOGlider, as the software is now called, breaks the terms of the license players agree to abide by when they run World of Warcraft (WoW).
Despite this decision Justice Campbell did not side with Blizzard in its claim that MMOGlider broke the terms of the Digital Millennium Copyright Act.
MMOGlider is the creation of MDY founder Michael Donnelly and more than 100,000 copies of the $25 (?12.47) tool are thought to have been sold.
It has proved popular as it helps players overcome the "grind" involved in turning low level WoW characters into more powerful ones.
Blizzard launched the case in 2006 via a lawyer from Vivendi, which publish WoW, who visited Mr Donnelly at home accompanied by a private investigator who told him to stop selling the software and hand over profits from it to Blizzard.
"Offended" by these threats Mr Donnelly decided to take Blizzard on in the courts.
Unless Blizzard and MDY settle out of court the case looks set to go before a jury in September. This court case will decide some of the issues the Judge did not pronounce on and address the question of whether Blizzard is due damages.