Yesterday Blizzard announced that “when you are in the business of fun, not every week ends up being fun”. Blizzard has detected a security breach in their battle.net servers. The hackers were able to access North American emails associated with accounts, encrypted passwords, and the answers to security questions. Even though only encrypted passwords were stolen, Blizzard recommends that you change your password anyway.
We also know that cryptographically scrambled versions of Battle.net passwords (not actual passwords) for players on North American servers were taken. We use Secure Remote Password protocol (SRP) to protect these passwords, which is designed to make it extremely difficult to extract the actual password, and also means that each password would have to be deciphered individually. As a precaution, however, we recommend that players on North American servers change their password. Please click this link to change your password. Moreover, if you have used the same or similar passwords for other purposes, you may want to consider changing those passwords as well.
The whole article is here. Change your passwords everyone