U.S. citizens must report all income to the United States, even if that income is kept in accounts outside of the country. Anyone who has an offshore account is required to file an annual Foreign Bank Account Report (FBAR) to alert the treasury department to the fact that the account exists at a foreign bank.  If income is earned on offshore investments, taxes must be paid on it. 

The IRS rewards whistleblowers who come forward and report attempts to evade taxes.  One whistleblower received a record amount of money for reporting on the activities of UBS AG in facilitating tax evasion. That whistleblower is now assisting France with its own investigation into UBS and the testimony he provides is expected to significantly increase pressure on the bank.