July 5, 2011:
It's recently been revealed that unnamed Middle Eastern airlines are equipping their commercial aircraft (passenger and cargo airliners) with electronic sensors and cameras, so that covert spying could be carried out as the aircraft went about their usual business of transporting passengers and cargo. This is actually an old Cold War technique. The Soviet Union (Russia) was particularly paranoid about this, and harshly enforced flight paths permitted foreign airliners flying through Russian air space. In several instances, Russian interceptors shot down airliners that had navigation problems and wandered off their assigned flight paths.
These days, electronic sensors and high powered cameras are smaller, more powerful and easier to hide. The spying opportunities are most often exploited during over-flight. By international agreement, if a nation wants to fly into, or through, a foreign nation's air space, they have to allow a certain number of flights through their own air space. Thus Iran is vulnerable to this kind of spying, in order to operate their own international flights. North Korea, on the other hand, only allows a few nations to fly in, and doesn't care if it can't fly its own airliners to many foreign nations. The few nations that have over-flight rights in North Korea are China and Russia (traditional allies, but not so allied anymore.) China, in particular, may be using sensors on commercial flights to keep an eye, and ear on North Korea. The electronic eavesdropping equipment is particularly good at studying radars and electronic warfare equipment.
The U.S. does not need this commercial aircraft spying capability, because America has so many spy satellites. But for most nations, specially equipped airliners are a cost-effective substitute.