Banned Spammer keeps coming back

[Ruralinfo.net]

I have banned the same spammer several times in the last few days and they keep coming back..  For some reason when I ban them they do not show up on my banned list... I am guessing that they register again but they always use the same username...   When I ban someone, does it block their IP? Does the username get banned?  Here is a link...   This one is becoming a problem with the repeated postings..

http://rural-mail-talk.581397.n2.nabble.com/Re-thomas-sabo-charms-td7594028.html

[Pedro]

We ban the email address. Do you allow anonymous posts in your forum?

[Ruralinfo.net]

Yes, I allow anonymous posts...  It might be time for me to require registration.. Havent had many problems before, but this one has become a pain!  Question- If I start requiring users to register can those that posted anonymously in the past use the same username when they register? Thanks Pedro..