By day they are human, but in their spare time they become mythical heroes such as wizards, dwarfs and blood-elves.

Over the weekend, 15,000 of them logged out of "World of Warcraft," the world's biggest online game, to gather in a hall the size of an aircraft hangar in Anaheim, Calif., for the "big nerdfest" that is Blizzcon.

They were drawn to the Anaheim Convention Center by their love of the virtual worlds they inhabit.

Blizzcon is part video-game carnival, part trade fair and part religious pilgrimage, organized by Blizzard Entertainment, which makes "World of Warcraft" and the real-time science-fiction strategy game "Starcraft."

Almost 11 million people pay $15 a month to play "World of Warcraft," and dedicated fans flew in from 27 countries around the world to attend Blizzcon, where they can discuss the intricate details of Blizzard's games with the game-makers, get the chance to play new expansion packs before general release, dress up as their favorite characters and compete against one another.

At the opening ceremony, in reality little more than a glorified press conference, the atmosphere is intense and the noise deafening.

The screams reach a peak when Mike Morhaime, the Blizzard chief executive, takes the stage. He's a gentle-looking man wearing a blazer — and the crowd greets him like a rock star.

"We are on the eve of a historic event next month, and I don't mean the presidential election," he says.

The packed hall roars in agreement.

For this crowd, something far more important than electing the leader of the free world is taking place in November — "Northrend will be open."

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