Newb question - I got a spammers registering 5-10 accounts everyday. What to do
 

First of all, I'm new to this and want to make sure it's actually a spammer and not some hacker whos trying to take down my site. Does this happen fairly common? I got an anti-spam mod that I use and image verification for registering accounts which doesn't seem to stop him. Is there potentially any harm that he can do to my forum except just to post in it? I don't think he can even do because you need to have a minimum of so many posts to post in most of the forums. I just don't really get whats the point of registering all these bogus accounts, Different IPs every time.

I don't think he can do anything besides post spamming that is major. If it's automated registrations then you can add a mod to your forum that forces any new member to read a number of posts otherwise they'll get an error which does not allow them to go anywhere.

If it's human then there is nothing much you can do besides deleting the posts and banning him each time. I am sure he'll run out of emails to register with. Disable urls as well to discourage him from posting.

Try adding a secret question, this is more effective and will stop the majority of spam registrations.

^^ what he said. The question/answer seems to be more effective in stopping spammers from signing up. Make it a question/answer specific to the users on your site (if your site is about anime, make it an anime related question).

There's big money in it for the thugs and free advertising else they wouldn't put forth so much effort. You don't want them having access to your members nor your members' profile info either. It's our responsibilty to protect them. There are mods that will do just that plus -as others said- registration options.