#4 - Sept. 24, 2010, 8:07 p.m.
Making certain both your system - and your email are secure is the priority at the moment.
Those aren't the only ways these thieves come by your information, but it is the two most common.
When you scan, make sure your scanners are up to date, you are using at least one for virus/trojans and one geared towards adware/spyware, and use them individually full scans with the launcher up and a bit of gibberish in the password fields.
I'd also highly recommend looking into one of our authenticators for an added layer of protection.
Blizzard Store
http://us.blizzard.com/store/browse.xml?f=c:6
Mobile Authenticator
http://us.blizzard.com/support/article.xml?locale=en_US&articleId=26109