UPDATE, April 5: Iceland Prime Minister Sigmundur David Gunnlaugsson resigned today, according to the New York Times, after he was one of a multitude of current and former world leaders who allegedly used a network of shell companies connected to one Panamanian law firm to hide their assets around the globe. 
The scandal is a result of a massive data leak consisting of more than 11.5 million documents, involving more than 200,000 companies and more than 14,153 clients of Mossack Foneca, a Panamanian law firm, according to Suddeutsche Zeitung, via the Times.
Gunnlaugsson wasn't the only Western nation leader to be snared in the Panama Papers' fallout, according to the Times--Britain Prime Minister David Cameron was scrambling to contain leaked data that shows British-governed territories are also friendly havens for  hidden wealth, including for his family.
A massive leak of documents from a Panamanian law firm has revealed a vast network of shell companies used by economic and political elites from around the world to hide their assets, according to Bloomberg. Among those who have availed themselves of its services are the current and former leaders of Russia, Iceland, Argentina, Georgia, Iraq, Jordan, Qatar, Saudi Arabia, Sudan, United Arab Emirates, and Ukraine, according to Bloomberg. Organized crime leaders, dictators, entertainment celebrities and plain old wealthy individuals have also been named in the leak. 

The documents show that the company enabled activities such as money laundering, bribery, and circumvention of anti-bribery controls, according to Vox. For example, though Ukrainian President Petro Porshenko had promised to sell his Ukrainian business interests upon assuming office, the leak reveals he just transferred them to a shell company he controls. The documents also say that the Prime Minister of Iceland, Sigmundur Davíð Gunnlaugsson, owned debt from Icelandic banks that he negotiated with during the financial crisis. He is set to face a vote of no confidence from Parliament in response to these revelations. Russian President Vladimir Putin has also been linked to the firm: while his name does not appear in any documents, it does name close associates of him conducting deals that would not have been possible without his patronage, according to The Guardian. 

The data also reveals details of secret offshore companies linked to families and associates of Egypt's former president Hosni Mubarak, Libya's former leader Muammar Gaddafi and Syria's president Bashar Assad, among others, according to CNBC. 

Yet, the majority of the shell companies the firm set up were used for the much more mundane purpose of good old fashioned tax avoidance. An internal document said "Ninety-five per cent of our work coincidentally consists in selling vehicles to avoid taxes," according to Vox. 

The law firm that set up the shell companies, Mossack Fonseca, has denied any wrongdoing and added that it cannot be responsible for the actions of intermediaries like banks, law firms and accountants, according to The Guardian.