After selling 250,000 copies in two days, it was pretty clear State of Decay would do pretty well for itself. The open-world zombie 'em up passed 500,000 sales within its first week, publisher Microsoft Studios has announced, declaring it "the fastest selling original game ever on Xbox Live Arcade." The "original" bit is to exclude Minecraft, see.

What now? Undead Labs is still working on patches, apparently doesn't have too much to do on the PC edition, and making a sandbox mode. Beyond that, well, there's still its dream of a full-on zombie MMO, codenamed 'Class4'.

"Fortunately [the PC version has] been in development alongside the Xbox 360 version since Day 1, so we just need to integrate with the Steam platform and add native support for keyboard and mouse control," Undead Labs founder Jeff Strain told Microsoft.

That's more promising than the last mention, which said it wouldn't be coming "by any meaningful use of the word 'soon'." I'd lean more towards the original statement than this new one, though. Plainly Undead's focus is on improving the XBLA version for now though, especially with distracting troubles like the first update not working.

Strain said the studio's listening to fans, and that their needs "will largely guide our development priorities." On top of that sandbox mode, "designed to be a pure survival simulation."

Undead Labs had always planned to make a proper zombie sandbox MMO, releasing State of Decay to test ideas and tech--not to mention raise a little money. The studio has separately told Eurogamer that the dream codenamed 'Class4' is still alive, but far from settled.

"We cannot begin working on Class4 without a greenlight from Microsoft (who owns the IP, as part of the bargain that led to the funding and development of State of Decay) and a mutually agreeable contract," community director Sanya Weathers said.

"We have to agree on where we think the technology is going to be in a few years (since the game will take a few years to develop); we have to agree that we have the same goals; and we have to agree on how we'll collectively run and support the final game ... Those discussions are still in progress."