There are two basic techniques to stopping spam:
- Prevent the spammer from ever getting a chance to post their spam content -- with things like captchas or requiring moderator approval on first post, or automated spam-recognition tools, etc.
- Detecting and removing spam content quickly with the help of a human.
In general, because of the high annoyance factor with technique #1 -- and the high chance of false positives, and confusing new posters, DC has always favored mild captchas and early-stopping techniques, and leaned heavily on technique #2, with some custom code to help alert moderators quickly to suspicious stuff, and remove it expeditiously.
Usually this means that a spam message is posted and then removed within minutes due to a quick moderator -- but occasionally a spammer will sneak through while all the moderators are sleeping -- despite our odd and overlapping sleep hours

After the new forum upgrade settles in we will get some more tools in place to exterminate the spam varmin..