this feature is not security related perse, it's just a way to block
bots and web crawlers. The challenge is occurring only on public pages.

sections/error/index.php

     case '400':
       $Title = "Error 400";
       $Description = "Bad request.";
-      notify(STATUS_CHAN,'403');
+      notify(STATUS_CHAN,'400');
       break;
     case '403':
       $Title = "Error 403";