What just happened? Around six years after the Brad Pitt-starring movie (itself based on a book) was released, the World War Z video game finally launched last week. Since its arrival on April 16, it has sold more than one million copies across the PC, Xbox One, and PlayStation 4, and that’s despite some mixed reviews and not being available on Steam.

Matthew Karch, CEO of developer Saber Interactive, said the game had done especially well on the PC, where it joined the list of Epic Games Store exclusives. The store's twitter account yesterday tweeted that World War Z had already sold over 250,000 units.

“We are humbled and thrilled by the immense success so far of World War Z, especially on PC thanks to the tremendous support of the Epic Games Store,” said Karch. “Moving forward, we’ll continue to expand the game and its community with new improvements, stability updates and bonus gameplay content, beginning very soon with a special new mission for the Tokyo episode.”

Karch added that at its peak, World War Z had 70,000 people playing concurrently across all platforms during its launch week. He said that PC sales outside of the US had been particularly strong, with the US making up just one-quarter of sales.

World War Z is a co-op shooter in which up to four players can take on hordes of zombies. It’s been likened to Left 4 Dead, albeit in a third-person rather than first-person view. Thanks to the game’s Swarm Engine, hundreds of zombies can be rendered on screen at the same time.

According to Metacritic, World War Z has mostly mixed or average reviews, but it seems that isn’t affecting its sales performance.