Due to the high volume of spam we've had over the past few weeks, I have disabled the ability for guests to post. Sorry guys, I know it's a bother to have to register in order to post, but it's also annoying to be getting 2-3 spam topics on the forums every time we look, especially when a few of them are indecent.
Yes, we were using CAPTCHA. Either it's easy to break or there's some flaw in it because it's been working fine for months and suddenly broke a couple weeks ago. There's no other CAPTCHA mod for SMF that I know of at the moment, so this is just the way it's got to be.