the u.s. passed a new tax law in 2010 that required foreign banks to disclose the names and assets of all of their u.s. customers. most countries - with the exception of switzerland - complied. to avoid paying u.s. taxes, a record number of these customers have renounced their u.s. citizenship.
side note: 22,000 american customers of the bank credit-suisse have refused to disclose their assets, and the swiss bank has said that it will not honor the u.s. law. every person involved is at least a millionaire, and several are billionaires.