So you've been hacked. Unfortunately all of your characters are gone or changed, and your account has been suspended. This is not good news to hear. So you might be asking yourself, 'How did I get hacked'? Chances are:
You clicked on a link in an official-looking email, and entered in personal information
You clicked on a link from someone in the game, and entered in personal information
You visited a site that downloaded malware or a virus to your computer (key-logger)
These sites and links are known as "phishing" (pronounced fishing), and they're used to steal your account information. Once taken, they will change your password and use your account to farm for gold, as well as sell what gold you have. Remember, Blizzard will NEVER ask you for your account information. They already have it!
Once you've scanned your computer, removed the offending programs (if any), changed your password, and added an authenticator, you should be good to go. But remember a few key tips:
Don't click on a link in an email that is supposedly from Blizzard. If it doesn't end in battle.net, it's not official
Don't give out your account information...to anyone, not even friends
Don't share accounts
Regularly scan your computer for malware or viruses to keep it safe and protected
Good luck! If you've been hacked, myself and others in this thread are all too willing to assist you. Post below and we can direct you to better resources and help you understand what your options are.