I moderate a chat system that has a rudimentary ban application. Problem is, it is incredibly simple for a user to create a new account and start chatting right away again. It is hard to create some sort of privilege to chat, because of how the site works (one of the features is anonymity, so the amount of user stats we keep is fairly limited).
We've tried IP based bans, but those are easily evaded with the variety of free VPN services available.
What can we do in these sorts of situations? Do we just need to sit there, banhammer at the ready, like a horrible game of whack-a-mole? Or are there other options?