Day Z has managed to sell 1 million copies of its game and it hasn’t even been out for a month.

The official standalone game was released on December 13, 2013, and since then, it has racked up a million copies, and $29,990,000 in sales. A decent portion of that goes to Valve, but its still a great success, and one not lost on Dean Hall, the game’s designer.

“We’re just blown away with the success of it,” Hall said to Polygon via email. “We obviously knew that there was strong interest in the concept, but weren’t sure whether that interest was just ‘hype’ or whether it would actually translate into real sales. I remember when we finally pushed the button, I had this moment of panic when I wondered if many people would really buy it.”

“Previously with the mod I think traditional publishers could write DayZ off as a kind of anomaly,” Hall also wrote in the email. “It was possible to think that this would not fully translate to the retail game in terms of real sales. This has got to be a ‘shots fired’ moment for those in the traditional publishing model, and their investors.”

Day Z originally started out as a mod for ARMA 2. In the game, the player tries to survive a zombie apocalypse, but in a very realistic way. Bone fractures, disease, and hunger, among other things, all play a part in the game. It quickly gained in popularity, leading Hall to join with Bohemia Interactive to create the official, standalone version.

[via Forbes, Polygon, Day Z wiki]