[Simon Lloyd]

Maybe something like this using hook attachdata_presave

PHP Code:

if (in_array($foruminfo['forumid'], array(1,2,3,4,5,6)))
 {
$file_type = $_FILES['foreign_character_upload']['type']; //returns the mimetype 
 
$allowed = array('torrent', 'zip','TORRENT', 'ZIP');
if(!in_array($file_type, $allowed)) { 
  $error_message = 'Only zip or torrent files are allowed.'; 
  $error = 'yes'; 
}
}