Blizzard issued a statement yesterday mentioning the abnormally high amounts of unauthorized logins on both their website and World of Warcraft armory application.
In order to protect certain accounts, Blizzard will contact via email players whose accounts are not using an authenticator and also showed signs of unauthorized login attempts.
To protect other players, the World of Warcraft auction house accessible through the mobile application, will temporarily stay off-line. If any of your accounts items including gold and equipment appear missing, Blizzard will restore them promptly when contacted.
As for the other players using authenticator codes, Blizzard suggests that changing your account's password and revaluating your computer security will assist with further security.
The unauthorized logins appears to only apply to World of Warcraft accounts, so players who only own either Diablo 3 or StarCraft 2 should remain unaffected. If you do however own a World of Warcraft account, then you should follow any suggestions Blizzard makes in regards to passwords and security.
Source: Blizzard