http://en.wikipedia.org/wiki/Van_Eck_phreaking is the means of essentially viewing everything on someone's screen via the EM the monitor emits. It is said that Mossad has a van eck device the size of a normal suitcase that can view monitors from across a street. I actually believe it.

The same can be said for keyboards and mice as well, especially wireless ones. The solution is a faraday cage.