OK, I use OpenDNS as my dns server and the Network Shield it appears to block this before it even gets there.
My only comment is that whilst it does block and alerts 'silently' no normal avast audio visual pop-up window, just an understated listing at the bottom of the screen which disappears after about 5 seconds. The browser, Firefox 3.0.3 displays a page not found pop-up, see images.
So all in all I feel this is a very understated alert, perhaps too understated as it could go unnoticed by the user if they miss the list at the bottom of the screen, they might just wonder what the problem is with the page not found browser pop-up.