Wasn't there some articles some time ago about Microsoft doing research into Tempest/Van Eck (sp) radiation ? It was speculated at the time that they were going include software to "broadcast" their serial numbers so that illegal copies could be detected.
This was a suggestion by Markus Kuhn and Ross Anderson (at Cambridge University). The paper is at http://www.cl.cam.ac.uk/~mgk25/ih98-tempest.pdf "Our suggestion is that software packages include in their screen layout a few lines with a signal that encodes the license serial number plus a random value . . . a "software detector van" can be used to patrol business districts and other areas where software piracy is suspected. If the van receives twenty signals from the same copy of a software from a company that has only licensed five copies, then probable cause for a search warrant has been established." p.13