HELP!! Hacker keeps hacking site

[Jeff G]

Don't know how he is doing this & would like help if possible.

Hacker is from Hanoi, Vietnam got me twice so far, used different IP's

He creates a screen name & then he is able to log onto my admincp? How? All permissions are set for new users & the have no admincp access, but he does & give himself admin privileges! & then tosses code for streaming ads into my main forum page.

I have change name of admincp directory to a completely obscure name, is there anything else I can do besides that & ban his IP & email addresses?

Any help would be greatly appreciated.

I have checked all files via FTP & none have been changed, so he is doing this straight thru Vbulletin!!