If you have created any account for a Blizzard game or on Battle.net, you are advised to change your passwords immediately. The company has confirmed that the attackers have likely gained access to user email addresses and passwords. CEO and co-founder of Blizzard, Mike Morhaime, said that North American Battle.net passwords were also accessed, but they were all encrypted and scrambled, making it difficult to get access to your account. But just as a precautionary measure you should change your account password. There is no news about any billing or credit card info being stolen.
Source: Blizzard
