Pirates around the Horn of Africa have received more than $400m (£251m) in ransom payments over the last seven years, a new World Bank and UN report shows.
The study, entitled Pirate Trails, revealed pirates and kidnappers along the busy coast of East Africa have ransomed off captured people and vessels for around $413 million since 2005.
The financiers behind the piracy receive most of the cash, rather than the pirates themselves.
The money then is mostly invested into criminal operations, including arms trafficking and migrant smuggling.
Campaigners are calling for a financial task force to investigate the money laundering networks, not just to target the pirates.
The report's key findings suggest that financial kingpins collect 30-50% of the total ransom, with what it calls the "foot soldiers" receiving only a standard fee.
Co-author of the report Stuart Yikona said: "The international community has mobilised a naval force to deal with the pirates.
"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 report cited a greater concern over pirate financiers "investing in militias and military capabilities" in Somalia. These people also control 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," Yikona said.
"The proceeds are typically moved by cross-border cash smuggling, trade-based money laundering, bank-wire transfer and the abuse of the Money of Value Transfer Services."
The study highlights the effects of a piracy economy in impoverished coastal Somalia that has brought benefits, but also sharply pushed up living costs, due to the inflationary effect of the flood of ransom cash.
Up to 10 EU naval ships now patrol the waters off the Horn of Africa, which are some of the world's busiest shipping and humanitarian aid routes.
The mandate of the anti-piracy force, which started in 2008, was broadened earlier this year to allow it to attack suspected pirates in the Somali coastal region.