I make a lot of use of Google Analytics - Google has reasonable tracking for location of users so I can tell where users come from. I know it is not 100% but it gives an idea.

In the wake of Prism it is possible that more people will make use of networks such as tor for anonymous browsing. I have no problem with this, people can wear tin foil hats while browsing my site for all I care, but it will lead to more erroneous stats.

Is there any way to flag traffic as coming from TOR, so I can filter location reports not to include it, and to get an idea of the percentage of traffic which does use it?

Has anyone actually tried this?