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Mitt Romney has acknowledged that until 2010 he kept money in a Swiss bank account. Romney says he wasn't trying to hide the money and that he reported it to the government. He closed the account at a time when the federal government was in the middle of a major crackdown on offshore tax havens.
As NPR's Jim Zarroli reports, that crackdown has made it harder for Americans to hide their money overseas.
JIM ZARROLI, BYLINE: The amount of money hidden in offshore tax havens is staggering. The Tax Justice Network recently put it at as much as $31 trillion worldwide, but that's just an educated guess. By their very nature, tax havens are secretive.
REBECCA WILKINS: First of all, you don't have an offshore bank account in your own name.
ZARROLI: Rebecca Wilkins, of Citizens for Tax Justice, says American companies and individuals can hide their money by opening an account in the name of a foreign corporation and it's virtually impossible for the Internal Revenue Service to find it.
WILKINS: The tax havens have a history of non-cooperation with the IRS. And even if the IRS got wind of some Panama corporation, you know, they would go to the Panamanian government and ask, who owns this? And they would get no information in return.
ZARROLI: But in recent years, the tide has been slowly turning. In 2007, the federal government received a tip that the Swiss bank UBS was helping people evade taxes. The bank ultimately had to release the names of its American customers.
The government also offered amnesty to taxpayers with unreported accounts. They could avoid criminal prosecution by paying back taxes and a penalty. About 33,000 people have participated in the program.
Jeff Kolodny is a tax attorney.
JEFF KOLODNY: I'm still getting calls from people to get involved in this program, because I think they realize now that the gig is up.
ZARROLI: Many of those who have come forward defy stereotypes. Daniel Shaviro, of NYU law school, says really rich Americans don't tend to keep their money in Swiss banks. He says they can usually find legal ways to avoid taxes.
DANIEL SHAVIRO: The people who were doing this were not - were economically a level or several levels below Romney. This is not poor people doing it but kind of affluent people with their own businesses, say, cash businesses, things like that.
ZARROLI: As these people have stepped forward, the IRS has leveraged their cooperation to go after other people, says Rebecca Wilkins of Citizens for Tax Justice.
WILKINS: So when somebody comes in and tells the IRS, here's my Swiss bank account, the IRS doesn't stop there. They ask the taxpayer, well, who's the accountant that helped you? Or, who's the attorney that drew up the documents?
ZARROLI: The IRS then goes to the person's tax adviser or attorney and demands they turn over the names of other customers. The U.S. has been working with European and Japanese regulators, who have launched crackdowns of their own.
Then in 2010, Congress passed the Foreign Account Tax Compliance Act, imposing taxes on overseas banks that won't name their American customers. This has extended the crackdown beyond Switzerland to tax havens in the Caribbean and Asia.
Attorney Jeff Kolodny says, as a result, a lot of overseas banks won't accept any more American customers.
KOLODNY: I don't think you can get the same level of privacy and protection anymore from the Swiss accounts. And this is true worldwide, really. I think the days of bank secrecy are over.
ZARROLI: U.S. efforts have had other benefits, as well. The amnesty program has brought in about $5 billion in back taxes and penalties.
That's just a small fraction of the money estimated to be in offshore accounts. And there's still a vast network of financial advisers and tax attorneys around the world ready to help people who want to hide their money. Still, the current crackdown has at least pierced the veil of secrecy that once surrounded many overseas banks.
Jim Zarroli, NPR News.
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