Yeah, and there is not much you can do honestly, that is, without restricting your actual members. Flood limits only go so far and having really long ones can really tick off your members. You just have to watch your forums - and maybe install a plugin that alerts you of new registrations, so that you can stop a spammer before they start spamming.
Not really on a large level. You and your staff should be able to catch it fast and Trash it. There are plug-ins to help with it if your running a public board.
I have yet to be a target of spam, it seems whatever setups I use when I had phpBB, myBB, and now esoTalk seem to be working extremely well (that is to NOT say I haven't had any spammers signup, but they have been unable to make any posts).
If you need help with preventing them send me a message and I'll tell you what to use and how to use it 🙂
I have gotten hit with lots of spam (over a hundred messages in the span of an hour). I had to turn off posting in the affected sections entirely, close registrations and then set to work cleaning up. After that I installed Spamalyzer and started to configure/tweak it. (My spam went from 100 an hour to like maybe 2 getting through in a day. And after a week of tweaking... now I get like 1 bit of spam in a month.)
I use Spamalyzer on MyBB. It scans each post before being submitted and if it detects spam then it deletes it instead. I've configured it to a point where I think it's pretty fair. So I'm not too worried about it.
Plus, I've blocked 2 of the top spam producing countries (Russia and China) by .htaccess so many spammers just aren't accessing the site anyway.
Spam was never an issue for any of my successful forums. On top of having tightened forum settings, our server automatically blocks potential offenders without mercy.
Having secure security should prevent it. Change flood limit and limit new members being removed from Newly Registered Group by having an admin do it manually (new members have limited perms) You could also limit the length of new members posts and try a plugin to block spam