Bot protection is a hot issue currently. It seems that no captcha on it's own is enough to prevent bots. You should:

1. use captcha (I still think that FunCaptcha is best, but there are different opinions. reCaptcha is most certainly not secure: http://www.deathbycaptcha.com/user/login)
2. use CloudFlare or Incapsula (they try to catch bots too, but make sure you've configured it correctly. Your web server MUST block connections that don't come from their servers or you'll be hacked)
3. use NastyHosts.com service (you can enable that in admin panel)
4. review and use one of the list of addresses / IPs / hostnames used by bots that you can find on this forum
5. don't put too much coins on your account and make use of the safety limits in FaucetBOX.com Dashboard

But still, there are no guarantees that it'll be enough.