A Palm Beach, Fla., woman has pleaded guilty to failing to disclose income from money that she and her late husband held in a Swiss bank account at UBS and later transferred to Liechtenstein, and she has agreed to pay a $21 million penalty.

Mary Estelle Curran pleaded guilty Tuesday in the U.S. District Court for the Southern District of Florida to filing false tax returns for tax years 2006 and 2007, according to the Justice Department and the Internal Revenue Service’s Criminal Investigation division.

Curran, a U.S. citizen, maintained undeclared bank accounts at UBS AG in Switzerland and a bank in Liechtenstein, which she inherited from her husband in 2000, according to court documents. The accounts at UBS were held in the names of nominee foreign entities, including the Flognet Foundation and Norega Investment. The account earned income each year, which Curran failed to report on her 2001 through 2007 individual income tax returns.

Curran admitted in her plea agreement that her conduct caused a tax loss to the government of approximately $667,716. The value of all the undeclared foreign financial accounts owned or controlled by Curran exceeded $42 million in 2007, according to prosecutors. In order to resolve her civil liability for failure to report her foreign bank accounts, Curran has agreed to pay a civil penalty in the amount of 50 percent of the high balance of the accounts, which is $21,666,929.

“Offshore accounts can no longer be used to hide from the IRS and avoid paying the fair amount of tax,” said IRS Criminal Investigation Chief Richard Weber in a statement. “IRS Criminal Investigation is aggressively pursuing tax cheats – both domestically and internationally. We owe it to every American taxpayer to use all lawful means to identify and prosecute both those who evade their taxes and those who assist them in evading their tax obligations.”

Curran faces up to six years in prison. A sentencing date has not been set.