Morhaime and Blizzard were quick to state that the information was not enough for any hacker to gain access to a user's Battle.net accounts, though users should still take precautions. This hack affects users outside of China and Morhaime is also recommending that anyone using North American servers change their passwords. This typically includes users in North America, Latin America, Australia, New Zealand and Southeast Asia.
In the days following this announcement, North American server Battle.net users will be asked to change their secret question while Blizzard will also be issuing an update to its authenticator software, which is something that most players should already use. World of Warcraft accounts get hacked regularly with hackers trying to steal in-game currency and high-level items.
According to a statement from Blizzard, "We take the security of your personal information very seriously, and we are truly sorry that this has happened. Like all companies doing business online, it is not an uncommon occurrence to experience outside parties trying to illegitimately gain access to the operation's structure at some level."
If you play World of Warcraft, StarCraft II or Diablo III then I highly recommend changing your Battle.net information, mainly just your password and security question. With the amount of money that goes through these games from players, a hacked Battle.net server is something nobody wants to see.
Source: UPI.com - Blizzard reports hack of its game server
G4 - Battle.net Hacker, User Information Obtained