From the WSJ last year:

By LAURA SAUNDERS
June 5, 2015 9:41 a.m. ET

Crucial deadlines are approaching for millions of U.S. taxpayers who live abroad or have offshore financial ties.

For expatriates, the annual income-tax filing deadline is normally June 15, instead of April 15. In addition, all U.S. taxpayers with offshore accounts totaling more than $10,000 in 2014—regardless of where they live—have until June 30 to file FinCen Form 114, known as Fbar, a report giving details of the accounts.

The PananaPapers can be a huge mess not only for the rich but many other less wealthy people.
The penalties can be 50% or more.