spammer without being listed as user?

Just set up my cart again and in the logs i have several “spammers” from a few IPs and its only the first week online! I have this one that is listed as a user in the logs section under “content” but is not attached to a user under the users section of the cart. How did this happen and how do i eliminate him from the database?

here is what it says:

User: PoobbyDek

IP address:

i banned the ip already,