You should upgrade to 4.8.1
As far as unregistered uploads in Vb3 there are numerous threads but not one person can replicate this with any consistency. They just say he I have these unregistered uploads every now and then.
I had devised a theory that the sessions from
VB are causing a session cookie which is causing a half logged in state when that is the only cookie set. However this is only a theory and I can not replicate this on every install.
I have suggested some customer try adding this to the vb3.php file
if ( $authuser == "" ) {
setcookie( "sessionhash", "", time()-3600, $Globals['cookie_path'], $Globals['domain_path'] );
}
but whether that is a solution who knows.