Horn of Africa pirates have raked in up to $413m in ransoms since 2005, with most of it used to finance "global scale" criminal operations, a new study shows.
The joint study by the World Bank, United Nations and Interpol said on Friday that the pirates themselves get little of the money paid to them by international ship and cargo owners, with their financiers getting most of the take.
The money then is spun into criminal operations including arms trafficking, migrant smuggling, and to fund militias, as well as into legitimate businesses, it added.
A multinational effort is needed to disrupt and halt the flow of illicit money that circulates in the wake of their activities.
The study, "Pirate Trails", points to the need to go after the money itself, as it is laundered and used in other areas, and not just the pirates.
"The international community has mobilised a naval force to deal with the pirates," said Stuart Yikona, a World Bank financial sector expert and co-author of the report.
"A similarly managed multinational effort is needed to disrupt and halt the flow of illicit money that circulates in the wake of their activities."
The study paints a picture of an increasingly sophisticated industry operating mainly from Somalia.
It is based on interviews with government officials, bankers, local businesses and former pirates.
It says that pirates, hijacking vessels from small sailboats to oil supertankers off the busy coast of East Africa, have been able to ransom off their captives for between $339 million and $413 million between 2005 and 2012.
Between 30 and 75 percent of the money ends up in the hands of "financiers", with only a small amount going to the pirates themselves.
Most of the money stays in the region, with a substantial amount laundered through the trade in khat, a popular narcotic leaf in the East African region.
The study says there is evidence that pirate financiers have used their gains to establish their own stakes in the khat trade.
In addition, they buy heavily into real estate, and could be getting into oil trade, transportation, restaurants and hotels.
But it cited a greater concern over pirate financiers "investing in militias and military capabilities" in Somalia, running human trafficking operations, and other criminal activities.
"The fact that proceeds from piracy are being used to perpetuate other criminal activities is concerning for the development and stability of the region as a whole, and deserves increased attention from local and international stakeholders," it said.
The study paints a picture of a piracy economy in impoverished coastal Somalia that has brought benefits, but also sharply pushed up living costs, due to the flood of ransom cash.