Central Intelligence Agency (a U.S. government entity that began its life as a spy agency but which today undertakes all kinds of clandestine activities abroad, beyond spying). Considered by many abroad as a terrorist organization in its own right.[1]
[1] See these sources to get a glimpse into the range of activities that the CIA is engaged in (which are not all necessarily legal under both U.S. law and international law):
http://www.bbc.co.uk/news/world-us-canada-14745941;
http://www.bbc.co.uk/news/world-11469369;