This is especially true if you're using the same email and password combination as you use for your Battle.net account on other sites. A big way that players get hacked, especially those without authenticators, is that their guild forums get hacked, or their email gets hacked, or their Facebook. Once those username and password combinations are known, it's possible for hackers to try them in various different places, one of which might be your Battle.net account. So be careful, mix up your passwords, and in light of these recent security issues, consider changing your passwords.
It's also a good idea, again as a general rule, to get into the habit of changing your passwords fairly regularly, for everything. So now might be a great time to start, even though Battle.net is unaffected by the recent issues. Hit the break for Blizzard's full post.