Dota 2, the online action game currently in development at Washington studio Valve, has on at least one occasion topped the most-played charts on Steam.

The game is currently in a closed beta testing phase, yet at certain points in the past 24 hours it has managed to prove more popular than longstanding western hits such as Counter-Strike and Team Fortress 2.

In what is a testament to the game's international appeal, Dota 2 usually climbs above the competition during downtime hours in the US, and drips back down the chart as North America approaches peak playtime hours.

Valve has deliberately targeted a global audience for Dota 2, and last year operated a $1 million online game competition called 'The International', where teams across Asia and the US competed online.

Invites to a second $1 million tournament are now in circulation.

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Dota 2 is arguably an adaptation of Defense of the Ancients; a Warcraft 3 spin-off that became one of the most popular mods in the world.

Valve and Warcraft rights holder Blizzard Entertainment are currently locked in a legal dispute over the suggested 'Dota' trademark – an issue that makes it difficult to describe the game in a non-prejudicial manner.

Defense of the Ancients is considered one of the most popular mods in the world, with an historical popularity across Asia.