The DMCA broadly restricts circumventing, or bypassing, antipiracy measures. Blizzard had included such measures to tie its games to the Battle.net site and detect pirated copies.

The defendants in the case, Ross Combs and Rob Crittenden, reverse-engineered the Blizzard protocol using tools like "tcpdump" to listen to the software's communications with a game server. Eventually, their "bnetd" project let Blizzard games connect with unofficial servers, yielding benefits like faster response times.

The 8th Circuit also cited a contractual agreement that Combs and Crittenden OK'd when installing Blizzard software. That agreement prohibits reverse-engineering.