Dear WW: I posted a while back about commercial espionage,
in which emissions of monitor through a window could be
used to learn a competitor's secrets. The article I read said that effective curtains on windows were sufficient
protection.

From the Internet:
"Across the darkened street, a windowless van is parked. Inside, an antenna is pointed out through a fiberglass panel. It's aimed at an office window on the third floor. As the CEO works on a word processing document, outlining his strategy for a hostile take-over of a competitor, he never knows what appears on his monitor is being captured, displayed, and recorded in the van below."