Do you and/or your mods spend a lot of time weeding otherwise to keep your membership database free of medical, jewelry, porn and other "product" spam? Some BBs seem to be jammed with those types of links at the database level. Most of those never post though, so you have to look at the database or catch the notification at the bottom of the index page when they first join. The ones that really piss me off those are the porn redirects that look and mouse-over as something benign, then if you click, take you to porn portals.
Notice that I am not naming, or do I want any particular BBs named. I've just noticed this phenomenom other places and wonder how some can stop it and others who say they "want to" can't.