Blizzard's World of Warcraft series has sold 8.6 million units to date, according to NPD data.
The number incorporates the base World of Warcraft and Collectors Edition, as well as the expansion pack bundle Battle Chest and two standalone expansions, The Burning Crusade and Wrath of the Lich King, reports Gamasutra; every game in the series released since its launch in November 2004.
At retail, the core game sells for an average of USD 19.95, and expansions and compilations up to USD 39.95.
These figures follow the news that The Sims 3 sold more than 800,000 copies in its first month at US retail. Overall, the EA series is the best-selling franchise of all time, having shifted over 100 million games worldwide.
Meanwhile, Activision Blizzard's most recent World of Warcraft subscriber figures revealed 11.5 million users are signed up to the game, with those located in the US paying USD 15 a month to play online.
With the recent operator transition in China causing extended server downtime for the game however, the userbase is likely to have diminished, which could negatively impact on subsequent subscriber counts.