The IRS and the Department of Justice have been on a long campaign of trying to get banks to turn over information on U.S. accountholders. A program called the Swiss Bank Program divided financial institutions into four different categories, with Category 3 and 4 banks in compliance with U.S. tax laws and Category 1 and 2 banks suspected of aiding U.S. citizens in evading tax obligations.

In 2010, the Securities and Exchange Commission (SEC) brought charges against a billionaire named Sam Wyly. The SEC charges ended up resulting in a $300 million judgment in 2014.  Sam Wyly filed for protection from the bankruptcy court after the $300 million judgment. Unfortunately, the problem for Sam Wyly was that his SEC judgment and subsequent filing triggered a tax assessment for failure to pay taxes on the income he happened to have held offshore.

The U.S. tax system is a pay-as-you-go system, but most individual employees do not actually pay as they go. Instead, the responsibility falls on employers to withhold federal taxes and FICA taxes from employees. Federal income tax, as well as taxes used to fund Medicare and Social Security, are supposed to be taken out of an employee's paycheck. Employers have to file tax returns and pay the IRS with money that has been withheld, as well as make required employer contributions (employers pay half of a worker's Social Security taxes).  

Swiss banks used to be a good place for people to put their money offshore without worrying about the U.S. government finding out about it. This was because Switzerland had strong banking privacy laws. Now, however, the U.S. has been aggressively going after banks in Switzerland and many banks have chosen to participate in the Swiss Bank Program, which provides amnesty from criminal prosecution and reduced penalties if the bank pays a fine and turns over account details from U.S.-affiliated individuals.

The Panama Papers is the name given to a leaked database of the Panama law firm, Mossack Fonseca. The law firm is the fourth largest offshore firm worldwide and its focus is on incorporating offshore businesses and opening offshore accounts. The Panama Papers which were leaked include extensive details, including the names of accountholders and information on how corporations were created and how money was moved.