Bot bypassing verification code to Contact form and Forum Registration

[Nephile]

Hello! I would like some assistance in the following problem.

Just now, a (what I believe it is) a bot (named Atalanda) registered on my forum and posted a message advertising something(gold for a game). I thought it was a guest posting where they didn't have permission at first. Was wrong. It actually registered.

On Tue 19 Jul 2011 - 6:58 I received from Продвижение неизбежно an message sent though the contact form. I did a google search and this one seemed sent by a bot (same message appearing on a good amount of boards).

Both had weird e-mail addresses.
The forum is a few days old (why target an empty forum...mindless bots) and I still have those messages if you need them. Screenshots:
http://tinypic.com/r/o7q2it/7 - the one with the contact form
info about the one that registered - what it posted: http://tinypic.com/r/2e4dt7c/7 (moved to basket)
ip: 205.209.133.62 its e-mail: should I post it?.

I mention that the contact form has its verification code showing (Never believed that kind of code did much. Got that confirmed now) and the automatic activation of new accounts was on but the activation turned off by mistake. I'll change to confirmation of e-mail address and code right now .

I'm sorry if this message already exists here somewhere or is in the wrong forum. If it doesn't then I would like some security suggestions or something. It may be my fault somehow (for not checking the right options) but this shouldn't happen.
My computer is wild at this hour and almost crashes me or I would have run a proper search not a few pages one but my eyes aren't helping me at almost 6 AM (shouldn't make excuses, I know).