Undead Labs' open-world zombie game State of Decay has now sold more than 2 million copies since its original launch in June 2013. That figure includes the number of units sold across Xbox 360 and PC, but does not include sales of the game's add-on content.

　　State of Decay reached 1 million copies sold in October 2013. In a statement on the developer's website, the studio said it particularly had gamers to thank for the game's success, as marketing was not a big focus.

　　"There just aren't the right words to tell you how much this means to us," the developer said. "No marketing, no advertising, just you playing and streaming and spreading the word. You made this happen, and if we could individually thank each person who hit that download button, we would. Your enthusiasm and support have been everything. Thank you."

　　To mark the milestone, Undead Labs said it will hold a month-long celebration. Details about what this will entail were not shared, but the developer said it will release more information through Facebook and Twitter.

　　In January, Undead Labs and Microsoft announced a multi-year, multi-title agreement to extend the future of the State of Decay series. The first part of this is the State of Decay Year One Survival Edition, which is launching for Xbox One in early 2015. The game bundles in the two previous DLC releases (Lifeline and Breakdown), features 1080p visuals, and will introduce new gameplay elements.

　　Undead Labs is also working on a free-to-play mobile game called Moonrise.