WoW Insider has a good article that may go some way to allaying any fears about the security of the Blizzard Authenticator. This device basically allows two-factor authentication for your World of Warcraft account.
For those who don’t know, two-factor authentication means you have to provide two items to prove who you are to, for instance, the Internet site you are trying to log in to. In the case of an authenticator like this one, you provide both your password, chosen by you, and the random code provided by the authenticator, to log in. Since each code generated by the authenticator is unique each time it it used, someone who wanted to sneak into your account would have to actually have the authenticator in their possession AND know your password.
Authenticators like this are a really good idea, when used properly by the companies that implement them. I hope to see a lot more banks and credit card companies offering this kind of authentication in the future.
I know people who have had their accounts hacked, so I think getting one of these is really a great idea.