GAMES DEVELOPER Blizzard has notified gamers about an intrusion into Battle.net.
The firm has warned players of games such as World of Warcraft and Diablo III that email addresses and hashed passwords, but no financial information, have been accessed by hackers. It recommended that users update their accounts and change their passwords.
It said North American servers were attacked, meaning that players in that region and Australia, New Zealand and South East Asia are affected.
Blizzard said that cryptographically hashed passwords but not clear text passwords were stolen, along with the answers to users' personal security questions.
The firm said it does not believe that anyone will be able to access accounts using just this information.
Despite this, it has advised players to change their passwords for Battle.net along with any other similar passwords for other services.
It added that it has closed down the unauthorised access and is working with law enforcement to track down those responsible.
Battle.net has millions of players, around ten million of whom play World of Warcraft. In an open letter to players, the firm issued an apology.
"We take the security of your personal information very seriously, and we are truly sorry that this has happened," said Blizzard president and co-founder Mike Morhaime.
"In the coming days, we'll be prompting players on North American servers to change their secret questions and answers through an automated process. Additionally, we'll prompt mobile authenticator users to update their authenticator software. As a reminder, phishing emails will ask you for password or login information. Blizzard Entertainment emails will never ask for your password."
He added that the stolen encrypted passwords are protected by Secure Remote Password protocol (SRP), explaining that this should make it "extremely difficult" to crack them. µ