A former Swiss banker provided WikiLeaks founder Julian Assange with a database containing the bank account details of around 2.000 celebrities.
The data is not yet available on the WikiLeaks website, and it consists of two discs that Rudolf Elmer showed at a press conference in London.
Assange has promised full disclosure, as soon as the reliability of the information is verified, the BBC reports.
Elmer will appear in a Swiss court on Wednesday on charges of breaching banking security law.
The banker who previously provided information to WikiLeaks was fired from the Julius Baer bank back in 2002.
The forwarded data contains details of multinational financial firms and wealthy individuals from many countries, including Great Britain, the USA, and Germany and refers to the period from 1990 to 2009, as reported by the Swiss Der Sonntag.
"As soon as we saw the data, it was a revelation," Assange said.
A family under pressure
Elmer said that he is "against the system", and that he knows "how the system works" and how the money goes to offshore accounts.
"I've done that job and I know what's being done every day," he said, explaining why it's important for him to identify himself as a source.
The banker, who was head of operations for Julius Baer Bank in the Cayman Islands, said his family had been under pressure since he decided to disclose the information.
Elmer noted that he had spent 30 days in a Swiss prison for violating banking regulations, and had been offered money and the charges against him dropped, just to keep quiet.
The file that Elmer handed over to Assange, among other things, contains the offshore accounts of about 40 politicians in 3 banks.
The banker said that his wife offered the information to German Finance Minister Pir Strejnbook, but her letter was never answered, even though she did not ask for money.
Elmer, who runs a "whistleblowing" website with his wife, said that the information comes to him from several sources who wish to remain anonymous.
"I take charge of the whole thing," said Elmer.
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