Confessed mass killer Anders Behring Breivik testified in Norway on Thursday that he played "World of Warcraft" for 16 hours a day in 2006. Breivik is in court in connection with last summer's attacks, in which Breivik killed eight people by setting off a bomb in central Oslo and then shot 69 others to death on the island of Utoya.

Here are some details about the game:

WHAT IT IS: "World of Warcraft" is a popular series of online role-playing games. Millions of people form a virtual universe and become such characters as orcs, trolls, humans and dwarves. Among other things, characters battle dragons and monsters in the game and interact with one another. They improve by collecting virtual goods such as weapons along the way.

PUBLISHER: It is made by Blizzard Entertainment, a unit of Activision Blizzard Inc. The "World of Warcraft" franchise is one of the top money-makers for the company, though it isn't as lucrative as the "Call of Duty" series.

USAGE: "World of Warcraft" had 10.2 million subscribers at the end of 2011. It's recognized by Guinness World Records as the most popular subscription-based massively multiplayer online role-playing game, though that was based on a higher subscription total of more than 12 million in October 2010.

UPDATES: Although the game has been out since 2004, Blizzard has sold three updates to help keep it fresh. The latest, "Cataclysm," sold 3.3 million copies within 24 hours. Blizzard makes money from one-time sales of the updates as well as recurring subscription fees. A fourth update, "Mists of Pandaria," is in the works.

BEYOND GAMES: A live-action movie based on the game is in production. There are "World of Warcraft" comic books and a parody on "South Park."