bnetd is a software package that was reverse engineered from Blizzard Entertainment's Battle.net online multiplayer gaming service, providing near-complete emulation. The software allows users to create and play on their own servers, instead of Battle.net servers. Released under the terms of the GNU General Public License, bnetd is free software.
Due to a United States lawsuit won by Blizzard against bnetd's original developers, they no longer maintain or host bnetd.
CD key non-interoperability
Blizzard games are packaged with unique codes. CD keys are entered, but not verified, during the installation process. Connection to battle.net is permitted only with a valid and unique key. Individual keys are regularly disabled by battle.net administrators to block suspected cheaters from battle.net. Players with invalid or disabled keys remain able to play independently of battle.net, such as in single player mode, or through a direct connection to another player.
Blizzard, citing security and piracy concerns on their webpage about emulation, does not allow battle.net to interoperate with bnetd servers to verify CD keys. Because of this, bnetd servers do not implement battle.net's validation. This allows players to access full multiplayer functionality of Battle.net capable games without a valid CD key, by connecting to a bnetd server.
Blizzard takedown demand and lawsuit
In February 2002, Blizzard filed a DMCA safe harbor takedown demand against bnetd with their Internet service provider (ISP). Blizzard subsequently filed suit against the developers of bnetd and their ISP in the United States District Court for the Eastern District of Missouri. The lawsuit alleged copyright infringement, trademark infringement, and violations of their games' End User License Agreement (sometimes referred to as a clickwrap license) and DMCA anti-circumvention prohibitions, in what would become an important test case for portions of that law. The Electronic Frontier Foundation mounted a defense, in which defendants denied copying any portion of battle.net or Blizzard games, denied the validity of the battle.net trademark, denied that CD keys are an anti-piracy measure, and denied that bnetd is a circumvention tool.
In September 2004, the court disagreed and granted summary judgement to Blizzard. On appeal, defendants argued that federal copyright law, which permits reverse engineering, preempts California state contract law, upon which the EULA's prohibition on reverse engineering is grounded.
In September 2005, the Eighth Circuit Court of Appeals rejected the defendants' argument and affirmed the lower court's decision. "Appellants failed to establish a genuine issue of material fact as to the applicability of the interoperability exception [of the DMCA]. The district court properly granted summary judgement in favor of Blizzard and Vivendi on the operability exception." The appeals court further ruled that bnetd circumvents copy protection in violation of the DMCA.
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