Satellite signals on position, course and speed are typically sent from onboard navigation systems with no human input. Others, like arrival time, are input by crew.

Peter Blackhurst, head of maritime security at Inmarsat, which provides satellite communication services, said a ship could get its Global Positioning System (GPS) to give false data, including pretending to be another vessel.

“That equipment is programmable one way or another,” he said, adding that he had come across data manipulation by ships involved in illegal fishing or waste dumping.

Syrian-owned Lady Rasha’s satellite track first mixed up with the Iranian-owned oil tanker Millionaire on October 20, when the tanker began transmitting the same signal as the cargo ship.

Lady Rasha was then docked in Benghazi, Libya. The Millionaire tanker was sailing in the Indian Ocean.

To do this, the Millionaire changed its MMSI, a message that contains both location and identity data, from 572450210 to match the Lady Rasha’s number: 677030700.

Although the Lady Rasha sent signals during its journey across the eastern Mediterranean, its identity was overwritten by the Iranian ship, which was also sending position signals of its own from the Indian Ocean.

As a result, the Millionaire appears to be undertaking two parallel journeys thousands of miles apart, while the Lady Rasha’s track is not plotted.

On one track the Millionaire can been seen sailing the Lady Rasha’s course in the Mediterranean, and on the other it is powering though the Indian Ocean from east Asia back to Iran.

However, another piece of identification data, the IMO, can’t be changed, and that, too, is sent with every message on position, which enabled vessel-tracking experts to detect that signals came from two different ships.