The UK's Bureau of Investigative Journalism (BIJ) found that four of the biggest US technology groups collectively hold an estimated $124 billion in US Treasury debt, much of it offshore, earning them tax-free interest.
They cannot bring the money home where it can be used to help the government pay its debts because it would trigger a tax bill, so the companies keep it offshore.
US companies say a "territorial" type of tax system would avoid double taxation and ensure all businesses compete on equal terms. Of course, it would also encourage companies to shift profits overseas.
But the status quo is equally strange in that the US government appears to reward companies for their tax avoidance.
A senior international tax policymaker told the BIJ that US taxpayers paying interest to digital giants investing in US bonds was "a bizarre situation".
There is growing concern that the huge cash mountains held by the world's biggest companies represent a threat to global financial stability. Over a thousand of the biggest US non-financial firms hold $1.48 trillion in cash, reported Moody's, the credit rating agency last September. Over one fifth of the US corporate cashpile is held by Apple, Microsoft, Google and Cisco.