Hackers have attacked the online adventurous game World of Warcraft, which is owned by Blizzard Entertainment, a division of a division of Activision, killing all the virtual characters in major cities of the game.
Hackers are supposed to have developed a character capable of destroying those of other players and those controlled by the game.
Blizzard Entertainment community manager Nethaera said that certain realms were affected by an in-game exploit, resulting in the deaths of player characters and non-player characters in some of the major cities.
"This exploit has already been hotfixed, so it should not be repeatable. It's safe to continue playing and adventuring in major cities and elsewhere in Azeroth," Nethaera said.
"We are taking this disruptive action very seriously and conducting a thorough investigation."
The game has been played by more than 10 million subscribers, with half of the total expected to be in China.
The number of subscribers for the game have declined to 9.1 million at the beginning of 2012 from a peak of 12 million in 2010, while have again increased since the launch of an expansion called the 'Mists of Pandaria' in September 2012.