The crawler has no recursion depth limit. A site with dynamic parameter manipulation can cause an endless loop. This loop will block the crawler thread and use permanent server resources. Too many blocks can lead to a denial of service. The same site will be indexed more times and the search results will display the same site many times. This can be abused for spamming the search results. Exploit to test the endless loop: /* loop.php */ <?php $numb = rand(); echo $numb.'<br><a href="loop.php?value='.$numb.'">click me</a>'; ?>