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.
Elmer, who faces a trial in Switzerland for having compromised bank secrecy laws, was dismissed from Swiss bank Julius Baer as chief operating officer at Cayman Islands in 2002.
Der Sonntag, a Swiss newspaper, reported that the data includes account details of multinational companies, financial firms and wealthy individuals, including politicians, from around the world and covers the years 1990-2009.
Assange noted that some information on the discs would probably be handed over to certain British authorities, including the UK's Serious Fraud Office.
At a press conference in London, Elmer defended his decision to release the data by stating: I'm against the system. I know how the system works. I've been there. I've done the job. I know what is the day-to-day business.”