The revelation that an ex-employee of HSBC Holdings Plc stole tens of thousands of its Swiss accounts is likely to give U.S. tax authorities fresh clues in their pursuit of wealthy tax cheats abroad.

“To the extent the HSBC data includes U.S. based taxpayers having interests in HSBC foreign accounts, it is a virtual certainty such information will be delivered to the U.S. government,” said Chuck Rettig, an attorney representing U.S. clients of UBS, HSBC and others who held previously undisclosed accounts.

An Internal Revenue Service spokesman declined comment.