Even if there are few readers in this forum stupid enough to follow the spam links they are targeting it. This may be because most search engines now detect and ignore "link farms" so they need their links mixed in with real content in order to get a better place in search results.

The forum should be altered to add the rel="nofollow" to all links posted in messages. At least until the user has reached a certain number of posts without having been reported.

That way these spam messages won't contribute to the spammers google rank in any way.

Wikipedia explanation http://en.wikipedia.org/wiki/Nofollow