Blizzard is reporting that certain pieces of information for North American Battle.Net users has been compromised due to a hacking incident this week. According to the post on the Blizzard site, financial information is not considered threatened but account passwords, email addresses, security questions and mobile authenticator data were taken.
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.
Read the entire post on Blizzard's site.