title: how to prevent vulnerability scanning
body: <p>I have a web site that reports about each non-expected server side error on my email.</p>
  
  <p>Quite often (once each 1-2 weeks) somebody launches automated tools that bombard the web site with a ton of different URLs:</p>
  
  <ul>
  <li>sometimes they (hackers?) think my site has inside phpmyadmin hosted and they try to access vulnerable (i believe) php-pages...</li>
  <li>sometimes they are trying to access pages that are really absent but belongs to popular CMSs</li>
  <li>last time they tried to inject wrong ViewState...</li>
  </ul>
  
  <p>It is clearly not search engine spiders as 100% of requests that generated errors are requests to invalid pages.</p>
  
  <p>Right now they didn't do too much harm, the only one is that I need to delete a ton of server error emails (200-300)... But at some point they could probably find something.</p>
  
  <p>I'm really tired of that and looking for the solution that will block such 'spiders'.</p>
  
  <p>Is there anything ready to use? Any tool, dlls, etc... Or I should implement something myself?</p>
  
  <p>In the 2nd case: could you please recommend the approach to implement? Should I limit amount of requests from IP per second (let's say not more than 5 requests per second and not more then 20 per minute)?</p>
  
  <p>P.S. Right now my web site is written using ASP.NET 4.0.</p>