As a night person, I go the main page of the forums overnight, so I see the forums that have a spam message before the spam is promptly removed early in the morning.
Have you noticed that the spammers never spam "The Kitchen Sink?" They post to all the other forums but leave the most heavily trafficked one alone.
Why? Do the spammers think those Kitchen Sink guys have enough problems of their own without adding to their dificulties? Is there an unwritten non-intervention agreement among trolls to not intrude on other trolls' turf?
Any ideas on why the off-topic forum is spared?