Piracy is a crime as old as seafaring. In history as in literature, it conjures up an image of brigands with eye patches, pieces of eight and hearts of gold. In truth, it was always squalid, ruthless and barbaric. Europe was terrorised by the Barbary pirates from North Africa for a century; Blackbeard tortured and mutilated those captured during his reign of terror in the Caribbean.

There is nothing romantic about modern-day piracy either. The seizure of ships off the Gulf of Aden is maritime terrorism. The hijackers hunt in packs on speedboats, using rifles and rocket-propelled grenades to force their way on board, seizing the crews and forcing ships and their cargos to divert to their strongholds off the Somali coast. Using satellite phones to co-ordinate their attacks from a mother-ship - usually a hijacked fishing vessel - they have become increasingly bold in picking off vulnerable craft: pleasure boats, cargo ships and any vessel that would yield a substantial ransom for its release.

The spectacular hijacking of the Sirius Star, a Saudi supertanker laden with oil worth $100 million, takes the operations of these Somali pirates to a new level. The ship was some 450 nautical miles southeast of Mombasa, far from the approaches to the Red Sea where Western navies now patrol. Like most of the dozen ships taken to Eyl, the fishing port that has become the pirate headquarters, it was undefended. Its mixed crew had orders not to resist. It was a sitting duck.

There have been 83 attacks on ships off Somalia this year, with 33 vessels hijacked and more than 200 crew still held captive. More than 1,200 Somalis are estimated to be involved, with six major groups active at sea. Ransom demands have risen steadily, as shipowners have little choice but to pay up after lengthy bargaining. Most captured ships are not released for less than $10,000, and the opening demand for larger vessels is now $2 million. The gang leaders, protected as Robin Hood characters in impoverished and lawless coastal villages, have grown increasingly rich and sophisticated. Driving expensive cars and operating from new beach villas, they plan attacks with precision, stalking a new target after each ransom payment and ploughing back the money into new weapons and boats.

They must be stopped. The stranglehold on the world's busy shipping lanes is pushing up insurance costs, risking lives - nine crew have been killed in attacks and nine are missing - and giving terrorists linked to al-Qaeda a robust income and a deadly way of striking at the West.

The European Union has already mobilised patrols, and Nato has been given the task of protecting the seas, with the Royal Navy taking the lead. But new laws, new rules of engagement and new strategies are needed. US warships in the Gulf may need to be mobilised, not least to escort shipping bound for North America through the most dangerous waters. Authorisation for the use of force against armed raiders and their bases must be radically streamlined, and captured pirates must be made to face justice, however harsh the local laws. Negotiations must not degenerate into the paying of Danegeld: however risky, more rescue operations such as that carried out by the French should be considered.

Somalia is a failed state, lawless and bankrupt. It must not be abandoned. But its catastrophe must be stopped at its shores.