My forum is being absolutely flooded with Nokia for sale etc spam. I have a smart captcha that asks you questions, therefore these are not robots. Is anyone else having the same problem? I think i might end up banning all public email addresses.
look for similarities in the IP addresses. For example, everyone from India who signed up to my forum were spammers so I simply blocked all Indian IP addresses from the sign up page.
I will then lose a bunch of potential members. I would have thought they all use different IP's anyway.
I have managed to find this mod http://www.vbulletin.org/forum/showthread.php?t=131568&page=2 that will scan first post for keywords you define and if the post contains these keywords it will go into the moderator queue.
some forums have mods where the first 25 posts of a member have to be moderated before going live. Maybe something like this would benefit you.
These spamming putting this crap onto our forums is annoying. Captcha can be worked around when it comes to robots. It's not bullet proof. There is a mod for vbulletin so that you can put posts that contain certain words into the moderating cue so that they will only show on your forum once it's been moderated. Not sure what forum you are using, but maybe your forum will also have a similar mod.
The two combined - keywords plus new users with posts containing URLs going into moderation have worked wonders for keeping spammers from having an effect on my board.