The ruling, says US rights group the Electronic Frontier Foundation, delivers a harsh blow to the defence of fair use in copyright cases.
The action related to an emulator called "BnetD" which is based on a Blizzard game called Battle.net. This allows Blizzard game purchasers to meet on-line or on a local area network (LAN) to chat, find competition and start multiplayer games using the BnetD software.
In 2002, Internet Gateway, the ISP that hosted BnetD, found itself in receipt of a cease and desist letter from Vivendi, demanding that the ISP disable the web site hosting the BnetdD software.
Vivendi then sued, claiming that the programmers who wrote BnetD violated the anti-circumvention provisions of the Digital Millenium Copyright Act (DMCA) and that the programmers also violated several parts of Blizzard's End User License Agreements (EULAs), including a section on reverse engineering.
Judge Charles Shaw of the District Court for the Eastern District of Missouri agreed, finding late last month that the ISP and programmers behind BnetD were bound to the terms of Blizzard's EULAs and Battle.net's Terms of Use, and that by reverse engineering Blizzard software, creating servers that emulated Battle.net, and providing matchmaking services for users of Blizzard software, they were in violation of those terms.
The judge also ruled that, because the BnetD servers created a functional alternative to Battle.net and were used to bypass Blizzard's anti-piracy technology, "the defendants' actions constitute a circumvention of copyright under the DMCA".
"We consider this ruling to be a major victory against software piracy," said Mike Morhaime, president and co-founder of Blizzard. "By ruling in our favour on every count, the court is sending a clear message that creating unauthorised servers which emulate Blizzard's Battle.net servers is without question illegal."
The EFF, which co-represented the defendants, had argued that programming and distributing BnetD was fair use. The programmers reverse-engineered Battle.net purely to make their free product work with it, not to violate copyright, said the EFF.
"Consumers have a right to choose where and when they want to use the products they buy," said EFF lawyer Jason Schultz. "This ruling gives Blizzard the ability to force you to use their servers whether you want to or not. Copyright law was meant to promote competition and creative alternatives, not suppress them."
The EFF has confirmed that it will appeal the case, challenging the court's ruling that creating alternative platforms for legitimately purchased content can be outlawed.