Pirates operating off the Horn of Africa netted more than $400m (£251m) in ransom money between 2005 and 2012, a new World Bank and UN report says.
It says the financiers behind the piracy, and not the pirates themselves, collect most of the cash.
The money is then used to fund other criminal operations, including arms and human trafficking.
The report calls for a financial task force to root out the money laundering networks.
Its key findings suggest that financial kingpins collect 30%-50% of the total ransom, which rose to an average of $5.04m in 2011 from $3.67m in 2010.
But the “foot soldiers” receive only a standard fee amounting to $30,000 to $75,000 per ship.
The report says the local community in Somalia “provides goods and services to pirates, including food, repair services and khat”.
Khat is a legal stimulant in Somalia.
The report, Pirate Trails, says the financiers invest in both criminal activities and legitimate business interests.
It says, “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 report’s co-author, Stuart Yikona, said: “Unchallenged piracy is not only a menace to stability and security, but it also has the power to corrupt the regional and international economy.”
The report recommends increased monitoring of the financial flows from piracy, improved cross-border controls and better regional co-operation.
Mr 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 haul in ransom cash between 2005 and 2012 was put at between $339m and $413m.