Please help with filestore exploit

[CareyG]

I am sure you have all heard of the base64 exploit that is affecting hundreds of vbulletin users. I have had this base64 exploit for a while now. I had it last year and finally got rid of it after I updated my vbulletin but now it is back again. I have downloaded and installed this plugin which alerts you when your datastore plugins are affected. This is the email I get every morning when the exploit is injected into my forum. Can you help me out with this. What exactly does this mean and how are they injecting this code? I need to know how they are gaining access so I can stop it.

Datastore pluginlist mismatch!

================================================== ==============================
Plugin modified/added:
array (
'pluginid' => '3094',
'title' => 'vBSEO Cache Templates',
'hookname' => 'cache_templates',
'phpcode' => 'if(defined(\'VBSEO_ENABLED\')) vbseo_complete_sec(\'cache_templates\');