Wow! That's crazy.
This is one thing that I am quite ignorant on. How are they being hacked? It's not the result of running "third party" apps or anything as far as you know, is it? Or do you suspect they are brute-forcing their way in?
There are 2 ways. Back to the post on you not violating the rule on making a launcher. That used to be the big way. People making launchers that would save your username and password for you when you logged out. Some were Key Loggers.
Some figure that some mods have keyloggers in them. Kind of hard to fathom as you don't have mods loaded till you log in.
According to Blizzard most are coming from Trojan Virus, AddWare, or SpyWare with a keylogger in it. It doesn't just log WoW stuff it can log everything. Sadly what Blizzards says is that they are coming from invalid images or other links in Forum Posts. "Get wow gold here!!", "New WoW movie 3 mannning Onyxia", yada yada... Well people click the link get a popup but nothing happens or does it. Or the image or movie isn't what is advertised. But you're downloading a key logger. Popups from some of the poppular addon sites have been targeted for putting addware or spyware delivered trojans.
Personally I use PcCillin as my home antivirus and internet security software. I have since it came out in like 1998. Its one of the most comprehensive suites I have used. The latest version has active AddWare, SpyWare, Phishing, and other malicious activity detections.