There are two banking systems for the wealthy. Private banks. And “pirate" banks.

“Pirate banks” form a large and fast-growing virtual banking system that has helped the wealthy hide more than $21 trillion offshore, according to a new report from the left-leaning Tax Justice Network USA.

That hidden wealth is costing governments $280 billion a year in lost tax revenue, the report says.

The report says much of that wealth is held by fewer than 10 million of the global super-wealthy and is handled by the world’s 50 largest banks. Today's "pirate banking" clients include everyone from “30-year-old Chinese real-estate speculators and Silicon Valley software tycoons to Dubai oil sheiks, Russian presidents, mineral-rich African dictators and Mexican drug lords,” the report said.

“The ‘pirate banking’ system now launders, shelters, manages and, if necessary, re-domiciles the riches of many of the world’s worst villains, as well as the tangible and intangible assets and liabilities of many of our wealthiest individuals,” said the report.

The report was written by James Henry, a former economist for McKinsey & Co.

Of course, determining how much wealth is hidden overseas is an imprecise science. And many conservative groups contest the estimate.

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