In a statement posted on the Blizzard website, Mike Morhaime said: "This week, our security team found an unauthorized and illegal access into our internal network here at Blizzard".Email addresses for global Battle.net users outside of China have been illegally acquired, the CEO revealed.Answers to users' personal security questions, as well as information relating to mobile and dial-in authenticators, were also compromised. Scrambled Battle.net passwords for players on North American servers were also captured."Based on what we currently know, this information alone is not enough for anyone to gain access to Battle.net accounts," Morhaime insisted.Users are urged to change their passwords. A mandatory change to security questions is in the pipeline."At this time, we've found no evidence that financial information such as credit cards, billing addresses, or real names were compromised. Our investigation is ongoing, but so far nothing suggests that these pieces of information have been accessed," Morhaime added.The unauthorised access has been closed off.Blizzard did not reveal how many user accounts had been affected. The Battle.net service has registered details of more than ten million users, though the total sum is thought to be far more than this.The service, used for games such as World of Warcraft, Diablo 3 and Starcraft 2, features Secure Remote Password (SRP) protocols to protect passwords.Morhaime says the technology is designed to make it "extremely difficult" to extract user passwords."It also means that each password would have to be deciphered individually," he said."As a precaution, however, we recommend that players on North American servers change their password. Moreover, if you have used the same or similar passwords for other purposes, you may want to consider changing those passwords as well."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."We take the security of your personal information very seriously, and we are truly sorry that this has happened."