Previously, it thrived despite the presence of warships and patrol vessels of three Southeast Asian nations.

"It is still one of our piracy hotspots, but since December 26 tsunami we have not recorded a single attack on shipping in the Malacca Strait," Noel Choong, of the International Maritime Board (IMB) in Kuala Lumpur, Malaysia, said.

The IMB tracks incidents of piracy around the world.

"One reason may be that the physical assets they [pirates] use, the boats and the weapons, were destroyed in the tsunami. And, of course, the another possibility is that they themselves may have died. It's a big question mark and we're watching the situation closely."

Smugglers' island

More than 100,000 ships annually travel the narrow, 960km-long waterway that separates the Malaysian peninsula and the Indonesian island of Sumatra, carrying roughly half of the world's oil supplies and a third of its the cargo.

Located at the northern tip of Sumatra, Aceh is well known for smuggling, gun-running and piracy.

Indonesian navy patrol boats
policing the Strait of Malacca

Aceh's east coast was particularly notorious for the violence and sophistication of the attacks, which often involved several powerboats loaded with armed men who would strike in the early hours of the morning.

If they managed to board, the assailants robbed the crewmen, and forced the vessel's safe. In rare cases entire vessels and their cargoes have been seized.

Dozens of crewmen have been kidnapped and held for ransoms of up to $60,000 per person.

Indonesian authorities, who on Sunday wrapped up three days of talks with the leadership of the separatist Free Aceh Movement (GAM) in Finland, routinely accuse the rebels of engaging in piracy to support their 29-year military campaign.

Organised crime

While it might once have been the case, evidence collected from sailors kidnapped for ransom indicate a criminal syndicate is primarily responsible, according to IMB's Choong.

"In the beginning, about five years ago, it was GAM. However, in 2003 there were signs that it wasn't GAM doing it but organised criminal gangs," he said. "These are kidnap-for-profit operations, not separatists."

The tsunami might have wreaked
havoc on local crime syndicates

GAM relies on the theft of weapons from Indonesian soldiers' armouries, and gun-runners operating along the rugged coastline to fuel their rebellion.

In 2003, Indonesian police stumbled across a container-load of smuggled refrigerators full of automatic weapons traced back to a theft from a Thai army base three months earlier.

The IMB reported that 121 of the 445 attacks on commercial shipping in 2003 occurred in Indonesian waters, a 20% increase over the previous year.

Twenty-one seamen died, over 350 were taken hostage and 70 remain missing.

Roughly 70 cases of piracy were reported in the strait during the first nine months of 2004.

Sharp rise

"These were very serious attacks, involving multiple boats and men with automatic weapons, shots into the bridge, lots of bullet holes in the windows and crew members being injured and killed," Choong said.

"In 2003 there were signs that it wasn't GAM doing it but organised criminal gangs. These are kidnap-for-profit operations, not separatists"

Noel Choong,
International Maritime Board, Kuala Lumpur, Malaysia

The final quarter of 2004 saw a sharp rise in piracy cases, despite beefed-up naval patrols spurred by fears al-Qaida might commandeer a vessel and crash it into the port in Singapore, one of the busiest shipping hubs on the planet.

Security analysts pointed to a specific incident in 2003 during which a container ship in the Malacca Strait was boarded and piloted for several hours by a group of men who stole nothing from the crew and disappeared into the night, as a possible training run for a future attack.

Pirates' response

Till recently, US and Singapore
were conducting joint patrols

Last April, a senior US naval officer disclosed the outline of plans for the deployment of US Marines and Special Forces troops in the Malacca Strait, souring relations with predominantly Muslim Indonesia and Malaysia.

Together with neighbouring Singapore they formed highly publicised joint patrols in the Malacca Straits, sharing radio frequencies and approving the pursuit of pirates across national territorial waters. The pirates reacted by expanding operations, Choong said.

"Before the tsunami, the number of attacks was increasing noticeably despite the presence of the naval patrols, which was troubling to us," he said.

"They're highly mobile. They move up and down the coast to the most northern tip of Sumatra, they were heading further and further out to sea and even into Malaysian waters."