Rudolf Elmer, a former Swiss banker, has handed over two data discs containing sensitive details of the accounts of 2,000 prominent people to Julian Assange, the boss of Wikileaks.
Wikileaks has not yet published the data on its website, but Assange promised full disclosure once the data had been vetted.
"Once we have looked at the data... there will be full revelation," said Assange, who is currently out on bail and confined to the UK due to an extradition request from Sweden, International Business Times says.
Mr Elmer, 55, is a former executive at Bank Julius Baer, one of Switzerland's top private banks.
He said that many of those identified in the CDs have exploited bank secrecy laws to avoid taxation. However, he said he could not - and would not - reveal names contained in the CDs due to the complexity of the systems used to hide money and the difficulties in unravelling the real beneficiaries, according to Sydney Morning Herald.
Former US intelligence officer Scott Ritter believes that Ukrainian President Volodymyr Zelensky should flee Ukraine.