The waters off the Somali coast are the most dangerous in the world - accounting for a third of the world's pirate attacks.
http://news.bbc.co.uk/2/hi/africa/7734985.stm
How do the pirates seize the ships?
The pirates are very good at what they do.
They run sophisticated operations using the latest hi-tech equipment such as satellite phones and GPS.
They are also heavily armed with rocket-propelled grenades and AK-47s. The pirates are known to receive tip-offs from contacts at ports in the Gulf of Aden.
They use speedboats with very powerful outboard motors to approach their target. Sometimes the speedboats are launched from much larger "mother ships" on the high seas.
To actually hijack the ships, the pirates first use grappling hooks and irons - some of which are even rocket-propelled - and climb aboard using ropes and ladders. The pirates have also on occasion fired at the ships to scare them into stopping, so it is easier for them to board the vessel.
The pirates then sail the hijacked ship to the Somali pirate hub town, Eyl. There, pirates board the ship and they normally take the hostages to shore where they are normally well looked after until a ransom is paid.
Why can't the pirates be stopped?
Warships from at least nine countries are now operating in the Indian Ocean and the Gulf of Aden but this may have only shifted the problem.
The Sirius Star was attacked a long way south of Somalia. The targeted area now encompasses over a quarter of the Indian Ocean and so is impossible to police. The International Maritime Bureau is advising ship-owners to adopt measure such as having look-outs or travelling at speeds which would allow them to outrun the pirates.
However, the pirates move extremely quickly and often at night and so it is often too late before the crew have realised what has happened.
Once the pirates have taken control of a ship, military intervention is complicated because of the hostages on board.
There is also no international legal system for people accused of piracy, although some have been put on trial in Kenya, while one group was captured by French forces and taken to face justice in France.
Earlier this year, French commandos detained Somali 'pirates' soon after the release of 30 hostages
As long as Somalia continues to exist without an effective government, lawlessness within the country and off its lengthy coast will only grow.
Only a few pirates have been caught and arrested. The British navy has shot dead at least two after they tried to board a ship.
Why do the pirates do it?
For the money.
The pirates treat the ship, its cargo and its crew as hostages and hold them for ransom.
The rewards they receive are rich in a country where there are no jobs and almost half the population needs food aid after 17 years of non-stop conflict.
One estimate says pirates have received some $30m in the past year in ransom payments.
Obviously, they use some of this money to fund future operations - more powerful weapons, bigger, faster boats and more sophisticated equipment.
How does piracy affect people outside Somalia?
Unless they are involved in the shipping industry, the main effect is higher prices.
Shipping companies pass on the increased costs - security, higher insurance premiums, ransoms and extra fuel for longer routes - in their fees and so it eventually finds its way onto the high street.
Piracy is estimated to have cost the world an estimated $60 - 70m this year.
