Blizzard Entertainment announced its free-to-play card game "Hearthstone" has reached 20 million players.

Hearthstone was released six months ago but has surpassed the current number of World of Warcraft subscribers, which is around 6.8 million.

The official Hearthstone Twitter account tweeted the statistic today writing, "Thank you all for joining us in Hearthstone! We're going to need a bigger tavern!"

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On the other hand, Blizzard Entertainment didn't indicate how frequently those Hearthstone players are active. Since it's a free game, there's no problem for anyone to try a few rounds of the game.

Leading the current surge in interest was likely the single-player Curse of Naxxramas expansion that started rolling in July.

Hearthstone manages to make players come back regularly by knocking everyone down in the leaderboards at the start of each month. It's possible as long as players get to rank 20. Once here, they earn a new, colorful card back.

Blizzard will hold its annual event in November and will feature a lot of new things about the game.

The next game expansion will focus on adding a large number of cards to players' decks rather than a Naxxramas-like experience.

The game will also launch on mobile devices later this year.

TagsHearthstone, Blizzard Entertainment