Tor An anonymous Internet communication system is used to surf quiet anonymously through the net. Because of it’s anonymity it is also abused for illegal activity. Below you will find information about how you can denied access from Tor to your site and why this would be security by obscurity.
You can block access from Tor to your site based on a list whith known Tor “Supernodes” available at:
http://serifos.eecs.harvard.edu/cgi-bin/exit.pl?sortbw=1&addr=1&textonly=1
http://www.ahbl.org/docs/torbl.php
Here you will find ways how to get around such limitations: http://wiki.noreply.org/noreply/TheOnionRouter/TorifyHOWTO#head-bbc4ee58b36fa00aec7be6bc4bf19ddb86ba10b9
As you can see… it’s security by obscurity. Better use the time to secure your webserver than to block such traffic.