I have an email validation on my forum, but bots still able somehow to bypass it. Almost all of them don't post anything, just appear in list of members. I tried to register myself and I found out that UNLESS you click the link in the mail that system sends, you don't appear as a member, only where it says "awaiting moderation". I use SMF 1.1.11, BTW...
I do have a built-in captcha module and I have it on medium level of complexity. Though it seems too simple, so I might as well go to difficult level.
Speaking of captchas...I know that there's a special module with that name and it looks somewhat special. So when you were talking about "captcha", did you mean just ANY type of module that does the same thing or that particular type?
I don't know if there's a way to change a type of captch module in SMF...?