Just to clarify, the last forums were ASP driven and the reason we didn't have much spam is because we (as in the Layonara community) were just starting to grow. Right now, we're averaging 3-5 new users a day.
Now, with respect to how these new forums (vBulletin) handle anonymous posters is rather special and deals with the wonderful security technique known as
Captchas. So, if you logout and try to post an anonymous posting, you need to type out a special code that's presented in a funny looking image that's virtually impossible for any automated system to decipher. Thus, by entering in the code presented in the image you are verifying beyond a shadow of a doubt that you are in fact a single human being sitting behind some computer screen connected via the internet to our lovely forums. In fact, I believe you even have to do the Captcha thing when you register a new account with the forums.
So, in answer to your question: there is a very high probability that you will not ever see any automated spambot postings on this site and when coupled with our very capable forum administrators, anything that does somehow magically slip through the cracks; it will be handled relatively immediately.
I hope that answers your query.
Enjoy!
PS: Please note that just because these forums run on PHP and act in a similar fashion to PHPBB, they are in fact very very different from PHPBB under-the-hood.
