I'm a mod at a forum with about 530,000 members, and over 1.6 Million posts, and we have found that spammers are getting very creative as of late. Registration checks will get the bots, but the human ones get by them fairly easy.
Here is what we do to combat spam:
1. New user registrations do not get access to PM's or signatures until they are off of moderation.
2. New user registrations are all moderated for the first several posts. The exact number is not released to the membership because the spammers were getting too smart for that. A few valid posts to get thru the system, then spread their crap. Spammers can get by the registration checks, but they have a piss poor comprehension of the english language. Posts that contain structural errors, grammatical errors, or odd punctuation are almost ALWAYS spam. Sometimes spammers will attempt to evade moderation by copying previous posts that are valid and on topic.
These actions keep the spam that becomes public to a minimum if the posts in the moderation queue are all given much scrutiny.
This does require changing some usergroups around, but isn't too difficult to implement... And no more essay's for new user registrations
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