Someone managed to penetrate the company's systems and steal the contact information of many its users as well as a password file, the company revealed in a message posted on the site.
However, those passwords were encrypted, the message says, so it would be extremely difficult for hackers to gain access to them. Even if they tried, they would have to attempt to decipher the passwords one by one. Nevertheless, as a precaution, Blizzard is urging users to change their passwords immediately -- and that also goes for any accounts that use the same password.
The hackers got access to the email addresses of users of Blizzard's Battle.net online gaming service, which is integrated into games such as World of Warcraft, Diablo III and others. So far it doesn't appear the hackers got access to any credit-card information, real names or billing addresses, Blizzard President Mike Morhaime wrote.
While the hack compromised email addresses of global Battle.net users, it was limited to players outside of China. For anyone who had information stored on the company's North American servers (which actually includes players from several regions worldwide), the hackers also gained access to personal security questions, although Morhaime says that wouldn't be enough to gain access to an account.
However, account holders may get hit with phishing attacks because of the breach. As Morhaime writes, users should never send passwords or login information via email. Blizzard will also be prompting players to change their passwords and security questions in the coming days.
There's also a chance the hackers were making a grab for the virtual items players can buy and sell in Blizzard's various games for cash, InformationWeek reports. Blizzard opened a Battle.net auction house earlier this year where players can make real money by selling those items, but third-party auction houses have been around for years. However, the hackers would need to gain access to the accounts for this to be practical, and, again, that's unlikely -- at least with what we know about the breach so far.
Blizzard says it doesn't know exactly when its system was breached or for how long, but it's investigating in partnership with law-enforcement and security firms.