Source? I heard of this trick from Schneier, but I have not seen any documents saying the US government is using it. In my experience, 90% of the things people say were in Snowden's documents weren't, so I'm skeptical. https://www.schneier.com/blog/archives/2008/04/tracking_vehi...

it's been a while but check back in a few days. if i can find it again i'll post it here.