Where can I find a top-dowIn thumbnail sketch of anti-spam techniques?

[Pithecanthropus]

Hello all,

I am one of a dozen or so mods on a very heavily trafficked messageboard. Of late we've noticed a very considerable increase in spam, and are currently discussing possible countermeasures. I have a considerable amount of IT experience, although not with messageboard functions in particular (except as a member, and more recently as a moderator). I have some notions of what might be effective approaches, but I don't know enough about how vB works in order to know if my ideas make sense or nonsense. BTW we are only at vB 3.7.

We already are using Akismet, but a lot of spammers have been registering and posting anyhow. The posts come either as new threads, or as replies to existing threads. In the latter case they are often, but not exclusively, zombies revived by the spammer.

The most notable feature of spammers' posts is that they almost invariably provide one or more URLs--in fact, the posts often consist of little more than that. I would like to know if it's feasible to automatically do something like the following, perhaps on a nightly basis:

1. Check whether any new users have posted any OPs or threads that include URLs. The quality of being new is determined by a configurable post count threshold for that user.
2. For any such posts found, disappear the posts to a moderation area or spam queue.
3. Ban the offending users, and send them emails explaining why this was done.

Usually a registered user who is banned will email somebody to find out why they were banned, or in an attempt to ingratiate their way back in, promising to abide by the rules in future. But I can't imagine that very many genuine spammers would do this. This means, then, that anyone who does contact the administration to be let back in probably wasn't a spammer, and they probably just overlooked a clause in the registration agreement that says you can't post URLs until you pass the threshold.

So, is something like this easy to set up? Difficult? Impossible? Does this idea make any sense at all?