We're aware of the issue and looking into it. We've had reports about this same problem related to the main MacNN page as well. It's almost certainly got to do with some sort of ad that not playing nice, or is itself corrupted or malicious.
I've been looking for it most of the day, and it's never hit me. Jman, you're the first person in Texas to mention seeing it. Having some sort of idea which users (by region, at least) are actually seeing the warning will help us track down which ad is the culprit.