Sick of spam bots

[Assegoestiree]

I've been getting a bunch of spam that I have no way to filter - the form submittal bypasses everything on my server, and they're using random or fake IP addresses so they cannot be blocked that way. All that have been coming in are done by someone using an automatic tool to complete and then submit my form. Is there anything that can be done to stop it? Any other suggestions as they are a pain having to go in and delete, not to mention that they are then messages that count against my total. Oh, and another question, just what are these guys try to accomplish by posting this crap on my forum:

I didn't manage to find any affiliate links or whatsoever, and the ads look like they were put there by the hoster and not the guy who've created this crap.
I'm really tired of spam, but i love my forum, and i have alot of users that post there frequently. So i thought maybe i would even pay you for your services. Of course i'm talking about real specialists. Please PM if you're one of them

However, ANY help will be appreciated, i just need a solution, thanks.

 

[mrhtbd]

Get a new security system, and please, don't send anything here from your address book. It's probably infected.

 

[basskiller]

which script are you running for your forum?
if VB, then you have options