Blizzard has issued a security alert due to their battle.net network was recently hacked affecting the entire North American region. Also affected are anyone who plays on North American servers even if they are located in different regions.
They have sent automated emails to everyone stating for passwords and account details to be changed as soon as possible.
As of now Blizzard confirms no financial info has been stolen yet but other info was indeed stolen.
http://us.blizzard.com/en-us/securityupdate.html