Activision Blizzard continues to milk its major video game hit of the year with the debut of a new map pack today for Call of Duty: Black Ops.

The Call of Duty: Black Ops Annihilation map pack is now available on Microsoft’s Xbox Live online gaming service for the Xbox 360. The launch of the map pack is a pretty big event, considering the original game generated more than $1 billion in sales and has become the best-selling video game of all time since its launch in November. Activision Blizzard says that its Call of Duty map packs — sold for 1200 Microsoft points, or $15 each — are the best-selling add-on content on Xbox Live. They’re basically a license to print money and can keep a game alive for much longer than the typical sales cycle.

The map pack has four new multiplayer maps and a new Zombie-shooting level where players can shoot each other or blast apart zombies all day long. The company previously released its First Strike map pack in February and its Escalation map pack in May. That’s a faster pace than the release of map packs for the previous year’s game, Call of Duty Modern Warfare 2.

Annihilation should keep players busy as they await the next major game installment in the combat game series. On Nov. 8, Activision Blizzard will release Call of Duty Modern Warfare 3. That release will include the launch of Call of Duty Elite, a social network for the game series with options for premium subscriptions.

The map pack includes:

—  “Hangar 18,” located in the highly classified military base of Area 51, where gamers will fight through experimental weapons labs, the SR-71 test hangar and a mysterious autopsy room.
—  “Drive-In,” where players experience close-quarters combat through a 1960’s American drive-in theater, complete with a snack shack and a classic arcade.
—  “Silo,” where gamers can infiltrate a massive secret Soviet nuclear missile site under construction within a multi-level battleground.
—  “Hazard,” located on the cliff sides of Cuba, where gamers can explore a coastal golf course fit for a Dictator, and where stocked clubhouses and
manicured fairways meet snipers hidden in sand traps.
—  “Shangri-La,” the all-new Zombies experience, transports players into a mythical paradise overrun with the undead. Players will come face-to-face with new species of zombies and navigate through a labyrinth of underground caverns, all set within a legendary shrine lost in an exotic jungle.