I have made a patch to check.torproject.org to expose a JSONP interface that would allow people to have the user check client side if (s)he is using Tor.
This would allow people to embed a badge on their website (privacybadge.html) that congratulates the user of using Tor or warns him of non Tor usage with a link to torproject.org.
I can imagine privacy advocates having this deployed on their websites or systems that engourage users to connect to them anonymously.
Compared to what check.torproject.org does at the moment the risk does not change, it is erogating exactly the same service, just making it more useful and flexible.
Basically what it does is check if the ip doing the connection is connected through Tor. The web service will reply with a JSON encoded array that can be loaded from the user and display in the browser a nice looking badge.
You can see how this works on the live demo hosted here:
http://hellais.github.com/torcheck/privacybadge.html
I still need to finish the styling of the badge to contain links to torproject.org and generally make it cooler.
Also, the check.torproject repo should be moved to svn.
- Art.