[efes]

You need access to LANs themselves to get ethernet addresses which would easily map to people on many devices. De-anonymizing based on traffic in a cafe is going to be a bit more complicated than average for some users and the random passerby who accidentally connects.

Besides, how can I be sure the people I am tracking actually work for the NSA? I refuse to do blanket tracking just to catch a few criminals, that is unethical.