http://snippets.bentasker.i2p/posts/nginx/blocking-tor2web.html
The problem with this, is that they act as a trusted middleman, potentially putting unwitting user's privacy and security at risk For sites that are multi-homed onto both the WWW and Tor Hidden Services, there's also the risk of a duplicate content penalty in search engine indexes (because Google will still index the Tor2Web sites). Note that this implementation will only block those Tor2Web nodes that announce themselves, others won't trigger the block - in order to catch those, you need...