Western navies have, since September 11, 2001, taken a great deal of interest in tracking the movement of certain merchant ships. It is known that al Qaeda owns a small fleet of cargo ships, and other countries that support terror, or just gun running, have their own ships. Tracking hundreds of ships is difficult, even with space satellites, maritime patrol aircraft and agents in many ports (keeping track of who enters and leaves). Over the last year, there have been an increasing number of rumors that these suspicious ships are being secretly equipped with small electronic tracking devices. These can be installed several ways. Navy SEALs can approach the ship from under water, at night, and attach a tracking device to the hull. Some ships that have been searched by American Coast Guard or navy boarding parties,  provides opportunities to plant a tracking device in some out of the way location. The tracking devices themselves don't have to be high tech. Using satellite phone technology, GPS, and long lasting batteries, the devices can be programmed to send out a message every hour, or day, telling the CIA where it's current location is. There are other electronic ways to track these ships as well. It's possible for intelligence agencies to buy location information of maritime satellite phone users from the companies that provide the phone service. Such deals will be denied by everyone, but they are made all the time. Quietly. For a sum of money and with the understanding that such cooperation will not be forgotten in the future. Meanwhile, no secret tracking devices have been reported as found by ship owners, and none of the ships being tracked have been found doing anything really, really bad.