Following a year-long investigation, emails, bank records and client documents spanning from 1977 to 2015 were leaked to German newspaper Süddeutsche Zeitung.
They were then shared with the ICIJ, as well as BBC Panorama and the Guardian – both based in the UK.
[To read about the industry’s reaction to the leak, click here]
Friends and associates of Russian president Vladimir Putin were implicated for manipulating as much as $2bn (£1.4bn, €1.75bn) through a number of banks and shadow companies, according to the ICIJ.
The documents also reference offshore companies controlled by the prime ministers of Iceland and Pakistan, the king of Saudi Arabia and the children of the president of Azerbaijan.
In the UK, six members of the House of Lords, three former Conservative MPs and dozens of donors to political parties were named.
In addition, more than 30 people and companies blacklisted by the US government for their involvement with, among other things, drug barons and terrorist organisations were implicated.
Crawford Spence, a professor of accounting at Warwick Business School said: “That the global elite ensconce their money in offshore tax havens and byzantine corporate structures is nothing new.
“However, these latest revelations concerning Mossack Fonseca are novel in that they show how elites from different walks of life come together in order to avoid scrutiny of their affairs by state authorities and the public more broadly.
“Thus, we see that Mossack Fonseca deals with concert cellists and Russian gangsters, Middle Eastern dictators, celebrity life coaches and European heads of state, such as the Icelandic prime minister. That one shady law firm in Panama has such a broad and high profile client base really is astonishing.
“The firm itself has denied any wrongdoing, but anyone found to be on their client list will surely be feeling nervous about being shown to share legal advice with Colonel Gaddafi and Bashar Al Assad. Thus far, this has been a journalistic investigation, but national tax and fraud authorities need to look very closely at these documents.”
Hidden and manipulated
While most offshore services are legal and above board, the documents indicate that banks, lawyers and other peripheral professional services often fail to follow the letter of the law, with some offshore “middlemen” hiding suspect activity or manipulating records.
The investigation shows major banks are often central players in the creation of shell companies often in the British Virgin Islands (BVI), Panama, and other offshore tax havens.
Nearly 15,600 paper companies have been set up for clients by banks including UBS and HSBC in a bid to evade the tax man, the ICIJ has reported.
Officials from FIFA and Argentine football superstar Lionel Messi were also named in the documents.
According to the ICIJ report, Mossack Fonseca, which has branches in Hong Kong, Zurich and more than 35 other international locations, said in a written response that it, “does not foster or promote illegal acts”.
It added: “[…] allegations that we provide shareholders with structures supposedly designed to hide the identity of the real owners are completely unsupported and false.”
The firm also allegedly said the backdating of documents was “a well-founded and accepted practice” that was “common in our industry and its aim is not to cover up or hide unlawful acts”.
“The revelations emerging from the release of the files are staggering, and probably represent the biggest single advance in the fight to combat tax evasion in more than 40 years,” said Sean Wakeman, tax investigations partner at Crowe Clark Whitehill.
“We have seen many examples in recent years of overseas banks encouraging UK individuals with bank accounts to settle monies in offshore trusts and place monies in overseas bank accounts to side step EU savings directives (and withholdings of tax at source) or to get round the UK Swiss taxation agreement.”
Wakeman said: “Anyone in such a position must now take urgent action to make a voluntary tax disclosure to avoid hefty fines or even criminal sanctions.”
Three years ago, leading up to a G8 summit, the BBC reported that David Cameron had called on British offshore jurisdictions to get their “houses in order’ regarding tax treatment and transparency.
The territories included Bermuda, BVI, Cayman Islands, Gibraltar, Anguila, Montserrat, the Turks and Caicos Islands, Jersey, Guernsey, and the Isle of Man.
The full ICIJ report can be found by clicking here.
The BBC Panorama programme will be broadcast on 4 April at 1930 BST.