Where is the SpamAssassin or DNSBL for Web Spam?

[terra_t]

A lot of us thing that web spam is Google's problem, but many of us build systems that process untrusted URLs (for instance, social media sites, content aggregators, directories, etc.) There are services that are are aimed at blocking comment spam, but I'd really like something that, given a URL, tells me if the site is a "blight" site: for instance, not associated with Clickbank, Acai berries, stuff like that.

Does anything like this exist?

[Freebytes]

There was a site that existed to block forum spam. It was designed for PHPBB forums. Also, Wordpress has add-ons to block spammers. However, something that could be used globally would be nice. I wonder if you could somehow have a DNSBL for your .htaccess file. It could check the list based on the IP address and then block. If that is not an option, some plugin files for popular languages would be efficient as well. (.php and .rb) How would the site be made profitable, though?

Or, are you referring to blocking based on the URL? Instead of blocking the content coming to your site, you would want to block access to sites with bad URLs? Spybot Search and Destroy does something similar to this with URL blocking, but that is only client side. How would this work within your browsers without using the proxy features and then giving up your privacy about which sites you visit?