Piracy has been making a comeback in the last decade, mainly because of a surge in attacks off the Somali coast. In the last few years a massive international response to the Somali piracy problem has all but shut down the pirate gangs operating there. Yet worldwide piracy activity is up, mainly because of resurgence in small scale piracy against fishing boats, offshore oil field support craft and attacks on larger ships for the purpose of robbing or kidnapping some of the crew, not stealing the entire ship.
The increased attacks on smaller fishing boats is largely because of the growing prosperity among these “artisanal fishermen” caused by the rapidly increasing prices for fish, especially the popular fish taken off the coasts of some countries (like Ecuador). The artisanal fishing boats are no longer powered by oars and sails, with navigation via a cheap compass. These days there’s an outboard motor, GPS and cell phones or radio for keeping in touch with other boats and the family ashore. All these items are sought by the pirates, who can usually find buyers a few villages away down the coast. When there is enough pirate activity there were develop a network of brokers (“fences”) who will take the stolen engines and electronics and get them sold far enough away so the victim does not see his own stuff again and call the police. These small scale pirates usually do not kill their victims, as police tend to be more energetic about solving murders than robbery at sea.
The big time piracy is largely out of business because warship patrols and better security aboard large ships passing Somalia has made it nearly impossible to seize these vessels. Holding ships for ransom only worked initially because Somalia, a state without a government sine 1991, provided small ports on the coast of East Africa where pirates could bring the merchant ships they had captured, and keep them there, safe from rescue attempts, until a ransom could be negotiated.
Off West Africa, pirates have come up with another angle. These pirates, believed to be only a few well-organized gangs, target small oil tankers operating in the Gulf of Guinea (where Nigeria and its neighbors have oil fields). The pirates quickly board and seize control of a tanker at night. The crew is locked up in an internal space and the tracking devices are disabled. Then the tanker is taken to rendezvous with another tanker, which takes the oil from the hijacked tanker, along with the pirates and their other loot and makes for a port where oil brokers willing to buy stolen oil (at a steep discount) take the pirated cargo, pay the pirates, and perhaps tip the pirates off on another small tanker that could be hit.
The hijacked tankers, stripped of portable items of value and then set adrift, are soon found and the crew released. Normally, pirates attack merchant ships anchored near the coast grab all the valuable portables and quickly leave. This is considered armed robbery, although some pirates will kidnap a few of the ships officers and hold them for ransom. But this requires a good hideout and more resources. The pirates who steal oil cargoes require even more technical organization and connections. But because the payoff is so high (millions of dollars for a stolen oil tanker cargo), a growing number of skilled gangsters are being attracted to the business.
All this has produced something of a piracy revival. Piracy hit a trough from the late nineteenth century into the later twentieth. That was because the Great Powers had pretty much divided up the whole planet and then policed it. Piracy began to revive in a modest way beginning in the 1970s, with the collapse of many post-colonial regimes.
Note that what constitutes an act of piracy is not clearly defined. It essentially comes down to non-state sanctioned use of force at sea or from the sea. This could include intercepting a speedboat to rob the passengers, but that's usually just thought of as armed robbery. And something like the seizure of the Achille Lauro in 1985 is considered terrorism, rather than piracy. In the past some marginal states have sanctioned piratical operations, like the North African Barbary States, but that is rare any more. The trend, however, is definitely up.
Pirates usually function on the margins of society, trying to get a cut of the good life in situations where there aren't many options. This is usually in areas where state control is weakest or absent, in failing and "flailed" states (a flailing state is something like Nigeria, Indonesia, or the Philippines, where the government is managing to just barely keep things together, unlike a failed state such as Somalia, where there isn't any government at all).
The solution to piracy is essentially on land, where you go into uncontrolled areas and institute some law and order and remove the pirate safe havens. This has been the best approach since the Romans eliminated piracy in the Mediterranean over 2,000 years ago. Trying to tackle piracy just on the maritime end can reduce the incidence of piracy but can't eliminate it. In the modern world the "land" solution often can't be implemented. Who wants to put enough troops into Somalia to eliminate piracy? And flailing states are likely to be very sensitive about their sovereignty if you offer to help them control marginal areas.
A new industry has developed that attempts to "pirate proof" ships operating off Somalia. The most successful (and most expensive) technique is to put a small number of armed guards on each ship. That, and warship patrols, has greatly reduced piracy off East Africa (Somalia). But off West Africa (especially the Gulf of Guinea) the piracy threat is growing because pirates have found ways to get more valuables off ships before security forces (police, coast guard, or navy) can show up.