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

       $Title = "Error 400";
       $Description = "Bad request.";
       notify(STATUS_CHAN,'403');
-    break;case '403':
+      break;
+    case '403':
       $Title = "Error 403";
       $Description = "You just tried to go to a page that you don't have enough permission to view.";
       notify(STATUS_CHAN,'403');