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

@@ -17,7 +17,7 @@ if (!empty($_GET['e']) && in_array($_GET['e'],$Errors)) {
     case '400':
       $Title = "Error 400";
       $Description = "Bad request.";
-      notify(STATUS_CHAN,'403');
+      notify(STATUS_CHAN,'400');
       break;
     case '403':
       $Title = "Error 403";