Blizzard Entertainment has issued a security warning for all World of Warcraft players. According to the warning, the studio has been tracking an uptick in unauthorized logins via both the website and the World of Warcraft mobile armory application, with individual warnings being sent to any players who do not have an authenticator and whose accounts have recently seen unusual activity. Players in this group should check their emails for information about resetting and securing their accounts.
Aside from encouraging all players to take extra steps to secure their accounts, Blizzard has temporarily shut down mobile access to the World of Warcraft auction house as an added security measure. Customer service will restore any items or currency lost as a result of this action. There's no information that this represents any kind of mass hacking, but it's probably best to change your password and get an authenticator if you don't already have one.