My Discussion board is getting spammed with erroneous posts

This evening my discussion board went wild with dozens of posts in rapid succession. None of the post are relevant to my docs nor my business (they all appear to be customer service pages from fortune 500 companies...weird). I disabled the discussion board to stop the spamming but this is not a desired outcome. Is there anyway to block select users from posting on my discussion board? I can see who the spmmers are in read.me and could block them if there was a way.