See the picture below. This page will be shown when you are accessing “considered forbidden” website from Google’s search result. I don’t know the criteria of a website that will be considered “harmful”, better ask Google for it 😉
But I think the idea is good. By doing this way, Google will prevent a “newbie” to access those site. As you can see, there is no direct link from the “warning page” to the “destination page”. See the red square. You have to copy-and-paste manually the link to access your destination page (I don’t think everyone know the way to do this, especially the one who is not familar with such thing). So, you put yourself on the risk by doing that, not Google. Clever eh?