The trouble with the Somali pirates, is that they will proceed many 100's of miles off the coast, and they themselves will not be detected by other ship's AIS. But they are equipped with a receive only AIS, and the rest is history.
It's a bit difficult to convince naval craft that you have a good reason not to have your AIS running when 200 miles or more from the coast, but as you know, the results are seen every day. The stuff that makes it to the media, is just the tip of the iceberg.