As you said your forum has been violated. Read through the information below and follow the steps carefully. There is tons of information on vbulletin.org and vbulletin.com on how to eliminate malware. A simple search will get you there.
Sorry your having problems.
Double check your system by using the best practices listed below.
Then please read the following two blog posts:
http://www.vbulletin.com/forum/blogs...ve-been-hacked
http://www.vbulletin.com/forum/blogs...vbulletin-site
Also please see these recent security announcements:
http://www.vbulletin.com/forum/forum...-1-vbulletin-5
http://www.vbulletin.com/forum/forum...d-all-versions