I suggest you try the akismet module from here:
http://drupal.org/project/akismet

It can block known ips and email adresses before they are submitted as spam plus you can enter a delay after spam is detected. (anti spambot option)

I have not had any fake identities entered since I started using the akismet module.

And so far I only had 1 spam comment since february 5th and until this day.