Same sort of thing happened to me. I'm gone for a month, and I come back all like: "Waaagh! That's a LOT of viagra!" I spent about 3 hrs cleaning up spam and banning bots, then I setup proper anti spam features
On my first forum I had, I never knew about the anti-spam plugins I could've used to prevent the spam on my forum(myBB) So I went to sleep, then the next morning I woke, I had like around 20 new accounts created and like 100threads+ created with stupid Russian products or something Lol. Took me a while to sort everything out.
Ohh, I don't think I got any actual people trying to spam mine, maybe because it wasn't that big the community . But the online list had like like over 20+ Guests trying to get in when I improved my anti-spam lol.
Yeah, the same thing happened to me a few weeks ago. Hopefully it was only a single incident. There's a plugin called Fassim Anti Forum Spam, but I found out that after installing it some people weren't able to register on the forum. The plugin mistakenly recognized as spammers. You can try it, maybe it will work for you.
I get the occasional spam comment on my blog, but thanks to Wordpress automatically adding Akismet to every account along with the option to moderate each user's first post before it being added to the site, it's never been an issue.
My server log files tell me that spammers are bouncing off my htaccess blocks. I don't allow visitors from two countries because 99% of traffic from them has proven to be spam on my site and I ban bots that try to fill in a hidden field during registration, real people can't see the field and so they'd never try to ad junk to it.
I think all new forum owners have experienced this, and it can frustrating trying to keep spam accounts out. Luckily Key Captcha seems to be like the perfect solution for my forum, and I currently receive 0 spam registrations with it enabled.
If a forum can be found it will be spammed, and you need to protect yourself.
What these idiots don't realise is that they're shooting themselves in the foot. Adding one or two spam posts on a popular forum might bring in a little traffic, but they tend to bombard small, vulnerable sites. This just ends up chasing away the site's real visitors and no-one ends up seeing their ads. It doesn't help them with backlinking either because as a site gets swamped with spam it loses PR and relevance, so their backlinks become useless, even damaging. Kind of like a swarm of locusts: Swarm in - destroy everything - then die of hunger because there's nothing left to eat.