The optical method is also quite smart, if you happen to, say, have an activity LED wired to a bus without much of a filter in between. LEDs switch faster than

The optical method is also quite smart, if you happen to, say, have an activity LED wired to a bus without much of a filter in between. LEDs switch faster than you might have thought¹. This kind of thing is intelligence-agency home turf; they have decades of experience, not necessarily relating to computers. [1] Joe Loughry and David A. Umphress [2002] "Information Leakage from Optical Emanations." ACM Trans. Info. Sys. Security, Vol. 5, No. 3, pp. 262-289 <http://www.foo.be/docs-free/tempest/optical_tempest.pdf> http://www.foo.be/docs-free/tempest/optical_tempest.pdf>