Stategy Page on "Modern Piracy"

Found at Strategy Page as Sea Transportation: Taking The Measure of Modern Piracy:

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.
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Pirates usually function of 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 keep things together but is faced with serious problems and areas out of its control, unlike a failed state such as Somalia, where there isn't a government at all.)
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In contrast to the Straits of Malacca situation, the U.S. approach to piracy has been largely a police mission, without trying to deal with the land-side. Again, that would mean occupying Somalia. But there are some regional constraints on piracy. There seems to be little or no piracy in the Red Sea and Bab al-Mandeb. Apparently this was because the smugglers decided the pirates interfered with their business (by bringing in coalition naval forces), and so shut down any pirate operations themselves. The Somali pirates may be in for another surprise, as there's talk by the UN humanitarian assistance folks (who have been losing relief ships to pirates) of seeking international agreement on permitting anti-piracy patrols to "violate" Somali territorial waters!

Usually, it just requires that some state with a vested interest in putting a stop to piracy, and the power to act on its vested interests, decides that it's had enough and takes vigorous action.