Better, IMO, to just assume they read and listen to everything digital, and work around it.
http://www.theregister.co.uk/2001/05/31/what_are_those_words...
http://ben.reser.org/echelon/
http://webcache.googleusercontent.com/search?q=cache:drmJsXD...
Better, IMO, to just assume they read and listen to everything digital, and work around it.