Just how popular has Blizzard's hit MMO World of Warcraft become? We've always known that the game has had millions of subscribers. Now a new analysis of NPD Group sales numbers by Gamasutra reveals that since the game's launch in 2004 it has sold 8.6 million retail copies in the US.

The sales numbers include the original core game, the Collector's Edition, its two expansion packs (The Burning Crusade and Wrath Of The Lich King) and the Battle Chest collection. It's likely that Blizzard has sold millions more retail copies in Europe. Versions of the game continue to sell well in stores; the original game, the Battle Chest collection and Wrath of the Lich King were all in the top 10 best selling PC games in NPD's latest list for June 2009.