The standalone version of open world survival horror game DayZ has sold over three million copies since its launch a little over two years ago according to developer Bohemia Interactive. It’s an impressive feat for any title but even more so when you consider DayZ is still in the alpha stage of development.

Fans of the game can attest to the fact that DayZ certainly hasn’t taken the common development path. The title started life as a mod for ARMA 2 under the guidance of game designer Dean Hall. Bohemia Interactive – who also makes ARMA 2 – liked what they saw with DayZ and recruited Hall to join their team and build a standalone version of the game.

DayZ was released on Steam Early Access just over a year ago. The standalone title sold more than 730,000 copies in the first three weeks, more than a million in the first month and crossed the two million units sold mark within four months.

Sales are of course slowing down now but its performance is still quite remarkable.

DayZ has been stuck in alpha partially due to the fact that the development team decided to change the game’s core engine last year from the Real Virtuality engine to the Enfusion engine. Bohemia Interactive says the new engine will be able to utilize DirectX 11, boost the visual aesthetics and provide better tools for content creators.