I'm not sure you can make money off of them at all. They won't help you, they only really there to help themselves...don't think they even look or click on any ads or what not. Does your forum have those CAPTCHA codes at registration?
Just a heads up to you about your suggestion. That is where most of the spam bots are directing to anyway; that and the questionable drug sites. A few try to redirect to a page that will load a trojan on your computer so they can steal personal data. FOR THE THREAD STARTER... I moderate a forum for a friend and have it set up for verification before they can post. That way I can look at their website info and where they have their e-mail and can check that they are either not humans or are just there to spam their links. My usual procedure is to copy/paste the url into McAfee SiteAdvisor first to see if their website already has warnings on it. This will tell you a bit about them. Then I use one of the site evaluation programs (My favorite is dnscoops) with this info you can find their associations, any links, check what is indexed on google, yahoo, altavista, etc. You can check whois from there too. It isn't hard then to see what they are up to. If I must finally go to their site, I try to use a cached page first as going direct can be dangerous for your computer. AltaVista BabelFish helps with the language barrier. In order to get your forum back from these illegitimacies, you will have to switch to approval first then take some time deleting the fake users and their spammy posts. If it has gotten as bad as you say, then this will take a while but hopefully your real users will appreciate your efforts. Good luck
I had the same problem on the forum I setup for our local animal rescue. It was bad, kids come there and these low life scums would post links to xxx sites. I have since setup the forum to new user approval. Its usually easy to tell whom is a real person vs the usernames for spam. The next thing I did was a lifesaver. I installed a mod that I can bulk delete users. The spammers sign up, I can wipe them out as many as I want in one swipe. I do not have to even hurry to wipe them out, since they never get approved to post.
yeah, if your dumb anough to fall for "viaga this viagra that" its a bunch of buulllshit I get this in junk mail evetryday
yeah thats what i was thinking, just make the forum so full of ads that /register.php is nothing but ads. LOL