Change security question?

Well my account has been hacked 2 times, and i deleted my old email and changed it to one that is only used for wow. Now i know you cant change the account name, but if you merge the account with battle.net, you can change it to an email. Now im guessing who ever hacked my account could have found out my security question, does the security question that i can make in battle.net become my new security question and the old one is gone? Btw i had to call to get my account back, and finally does my battle.net info override the info that was on the wow account when it didnt have battle.net? I'm just freaked out since i haven't paid much attention to my account since this is my first year of college and im adjusting.