Blizzard Entertainment, maker of popular multiplayer online games such as World of Warcraft, Diablo and Starcraft, warned on Thursday that its internal network was breached, revealing scrambled passwords and email addresses.
Law enforcement has been contacted and an investigation is under way, wrote Mike Morhaime, Blizzard's co-founder and president.
Hackers obtained email addresses for users located outside of China for Battle.net, Blizzard's portal for its online games, and the answers to those users' personal security questions. Affected regions include North America, Latin America, Australia, New Zealand and Southeast Asia.
Some information relating to mobile and dial-in authenticators was compromised as well as cryptographically scrambled versions of the passwords belonging to players in North America, Morhaime wrote. The information is not enough to access Battle.net accounts.
"At this time, we've found no evidence that financial information such as credit cards, billing addresses, or real names were compromised," Morhaime wrote. "Our investigation is ongoing, but so far nothing suggests that these pieces of information have been accessed."
Blizzard uses a "secure remote password" (SRP) protocol to protect passwords. Morhaime wrote it would be difficult to decipher actual passwords, but the company is advising its North American customers to change their passwords nonetheless.
In the expectation that some users may receive phishing emails, Blizzard reminded users that it would never ask for their passwords.
A common security measure is to store cryptographic representations of passwords called hashes rather than the actual plain-text passwords. The longer and more complicated the password, the more difficult it is to decode using password-cracking programs. Simpler passwords may be decoded with enough time and computing power, however.
North American players will also be advised through an automated system to change their security question, Morhaime wrote. Players who use mobile authentication will also be prompted to upgrade their software.
"We take the security of your personal information very seriously, and we are truly sorry that this has happened," Morhaime wrote.
