The web site for World of Warcraft was offline for about an hour early Wednesday, as the game’s infrastructure came under heavy load due to a major expansion. Activity has been heavy on many of the game’s servers with the launch of a software expansion pack, The Burning Crusade, which adds new characters and substantially expands World of Warcraft’s “virtual real estate.” Users reported performance problems yesterday in the early hours of the expansion.

While the extra traffic briefly downed the web site and slowed some game servers, the problems seem to be minimal compared to some of historic downtime issues for World of Warcraft, suggesting that system upgrades have made a difference in the game’s performance. Game operator Blizzard Entertainment announced last week that World of Warcraft now has more than 8 million paid subscribers, including more than 3.5 million in China. The web site outage last night can be seen on this performance chart:

A dynamically updating chart of World of Warcraft’s web site performance is available. Netcraft offers a web site performance monitoring service that provides similar charts, along with e-mail alerts when an outage occurs.