Even if you have an authenticator, you will still get hacked if you don't practice safe web browsing.
For those who can't afford or think getting an authenticator is a lot of hassle, you can always follow these steps

1) There are a lot of con websites who claims to be Blizzard and send you emails, saying that they want you to click this link or give your username and password to verify details. Always remember Blizzard will never ask for your username and password, be it email or ingame. Careful when clicking email links.

2) Make sure your password is hard one to figure out. Change your password regularly.

3) Here's another great tip. When you key in your password, do not enter them in sequence. Always key them in non-sequence to fool keyloggers.

Example, if your password is abc123, you can enter 'c12' first, then move your mouse to before 'c' and enter 'ab', then move your mouse to after '2' and enter '3'

When you press enter, your password will be abc123
But to keyloggers, your password will look like c12ab3

Hope this helps.

Don't think that's very safe. There are ways for hackers to access data in your clipboard

You can get hacked if you use the AH also.