Basically, it can open a window into your computer. And any particularly unscrupulous member of staff could, y'know, go into your computer and retrieve things like your credit card details.
Just wanted to let you guys know. Please pass on the message if you feel so inclined.
Cross-Posted to girls_of_wow.
Edit: Okay. Didn't exactly think I'd get flamed for the warning. Just wanted to let people know what I'd heard, since it sounded a bit dangerous. A friend of mine is the one who told me, and explained to me. He's also friends with the person that writes that blog. He knows about this type of stuff. Thus far he hasn't lied to me, so I've deemed him a credible source.