GameSpy's closure left these performers without a big top.
When GameSpy's new owner decided it didn't want to be in the multiplayer server business any more Bohemia's games were left without a place to play. At the time CEO Marek Spanel said he hoped to find an alternate solution via Steam, but nothing had been written in stone. Now it's official: Arma 2, and all the happy smiling DayZ zombie mod goodness that goes with it, is on its way to Valve's platform.
"Due to the fact that Steam based matchmaking requires Steam to work, this update is only available through Steam," says Bohemia. "If you have purchased a retail copy of the game, please do not despair. As announced previously all Arma 2 (including DLCs and Operation Arrowhead expansion) keys may now be activated on Steam." There's even a handy walkthrough to help you through the process.
Some of Bohemia's titles - Arma 1, Cold War Assault, Take On Helicopters - won't work on Steam. Bohemia also recognizes that some of its playerbase would prefer to keep on using the non-Steam version of its titles rather than play in Steam's circus. "We have implemented a system to help host and connect to servers even without a functioning GameSpy," Bohemia promises, and if you want to know how that'll work, there's a full explanation over here.
Source: Bohemia Interactive