Blizzard...get hacked? Blizzard has never been hacked. Even the hackers and people who create botting programs have said: "Blizzard is bulletproof." There have been security breaches maybe, where encrypted information may have been leaked out (and Blizzard always warns its users to change their information), but there has never been a single case of compromising user information (login/password/credit cards) by Blizzard in the 16 years I have played their games.
It is very easy to get information from the player's end though, as there are plenty of idiots who use the same login/password for 14 different types of forums and their WoW account. Security on forums is so much more lax, hackers are able to fish out entire databases of login/password data at a time and just plug them all into different MMOs. This is how the vast majority of accounts (across any game) come to be compromised.
Authenticator is free, the protection it grants is amazing, but it isn't 100% foolproof. That said, I don't think there have been many cases if any at all of people's accounts being hacked while having an authenticator.