World of Warcraft is a massively multiplayer online role-playing game (MMORPG) developed and published by Blizzard Entertainment. It is the fourth installment in the Warcraft series, and Blizzard's first game in the MMORPG genre. The game takes place in the world of Azeroth, approximately four years after the events of Warcraft III: The Frozen Throne. Since its release on November 23rd, 2004, the 10th anniversary of the Warcraft franchise, the game has achieved massive levels of success. In December 2011, Blizzard announced that there were over 10 million active subscriptions to World of Warcraft around the world. It is currently the most popular MMORPG in the world.The game has received three expansion sets so far, with a fourth one in development. The first expansion set, called The Burning Crusade, was released on Januray 16th, 2007. The second expansion, Wrath of the Lich King, was released on Novermber 13th, 2008, and the third expansion, Cataclysm, was released on December 7th, 2010. The fourth expansion, called Mists of Pandaria, is currently in a closed beta testing phase.