In Blizzard vs. BNETD, Blizzard used the DMCA to prevent open source projects from interoperating with its software. Blizzard software comes with the ability to play multiplayer games online through their Battle.net service. In order to combat piracy, Blizzard requires users of Battle.net to have valid CD keys and prevented people using the same CD Key from connecting simultaneously. A group of users enjoyed the game but disliked Battle.net due to people cheating in the games. They sought to create their own alternative, resulting in www.bnetd.org. This site gave users with Blizzard software to connect and play multiplayer games through their server. This open source project was posted on the web and other people used and modified to code for similar purposes.

In interpreting this case, the court claimed that BNETD was in violation of several provisions and was not protected by the reverse engineering for interoperability exemption. BNETD did not check to see if the user had a valid CD Key before allowing them to connect to the server. The court interpreted this as circumvention, as BNETD allowed users to experience online multiplayer games with illegal copies of Blizzard software.

This case determines that plug-ins could be held responsible for their functionality when applied to pirated software. Had the plug-in been designed to bypass CD Key checks and then connect to Battle.net, the decision would make more sense. However, BNETD wrote the program to connect to their own servers, and just didn't happen to check to for a valid software copy. Holding plug-in writers accountable for license checking is a dangerous precedent. Open source developers won't want to write a plug-in if they can be sued for the misuse of their product in combination with pirated software. The right to author extensions to software and market them has been around for years before the DMCA and now has been compromised by the misuse of its provisions.