LONDON — When an encrypted message first flashed up on Bastian Obermayer’s screen, the German investigative reporter could have no idea that he was about to receive the biggest leak of confidential material the world has ever seen.

“Hello. This is John Doe. Interested in data?” the source asked. Of course, he was.

Via an encrypted messaging service, the whistleblower continued:

There are a couple of conditions. My life is in danger.

We will only chat over encrypted files.

No meeting, ever.

Obermayer didn’t know it yet but this clandestine approach was entirely justified. The anonymous source was about to expose some of the most closely held secrets of the world’s most feared and powerful men. Pissing off Vladimir Putin, Bashar Assad or the King of Saudi Arabia individually would make a sufficiently daunting opponent, but close friends or relatives of all three of them are listed in an unprecedented leak exposing the innermost financial workings of their families.

It should be emphasized that moving tens of millions of dollars into offshore bank accounts, which cannot be accessed by international law enforcement agencies or tax collectors, is not an illegal act—but it does rather suggest that the owners of those accounts didn’t want their private financial records to be published by newspapers all over the world.

Yet, that is exactly what has happened after somebody obtained decades of secret financial records from one of the leading offshore banking experts.

Mossack Fonseca is a law firm based in Panama that has advised thousands of clients from Chinese President Xi’s brother-in-law to British Prime Minister Cameron’s father. Many of these secretive savers may have nothing to hide but many of the world’s tax and fraud agencies have already demanded access to their account data.

Why would the families of African dictators have vast sums of money they didn’t want anyone to see? Why did American companies want to put their profits in secret accounts? What are the chances that so many of Putin’s close friends have gotten so enormously wealthy without corruption straight out of the Kremlin?

Some of the answers may be found in the data that was being offered to Obermayer. “Why are you doing this?” the Süddeutsche Zeitung reporter asked his source when he came forward more than a year ago.

“I want to make these crimes public,” was the response.

Obermayer asked how much data they were talking about.

“More than anything you have ever seen,” came the reply. Indeed, the leak included 4.8 million emails, 3 million folders, and 2.1 million PDFs.

That is many times more than the WikiLeaks cables, Pentagon Papers and Snowden documents combined.

The “Panama Papers” include 12 current or former heads of state, and more than 60 relatives of and associates of heads of state and other politicians.

Some of these people have been linked to no crime whatsoever, while others stand accused of looting their own countries for personal gain.

Many of these leaders had awkward questions to answer on Monday. While Russia's strangulated press meant the Kremlin was able to laugh off the leak and blame "Putinophobia" for the accusations that a $2 billion trail of hidden money led back to the Russian president, the leaders of functioning democracies were plunged into crisis.

Thousands of furious Icelanders took to the streets of Reykjavik demanding the resignation of their prime minister after it was alleged that he had invested in a secret offshore company in 2007 just before the global financial crash brought Iceland to its knees. Sigmundur David Gunnlaugsson never declared this hidden asset to the authorities—he later sold half of his off-shore company, which may have been worth millions, to his wife for just $1.

Gunnlaugsson, who stormed out of a TV interview when confronted about the investments, now faces a vote of no confidence in the Icelandic parliament although he denies breaking any law and refuses to resign.

In Ukraine, the opposition launched a campaign to impeach President Petro Poroshenko after it emerged that he had set up a secret off-shore company in the British Virgin Islands to protect his assets just as Russian tanks were rolling into the country.

When Süddeutsche Zeitung realized the scope and potential fallout of this leak, they enlisted the help of the International Consortium of Investigative Journalists, based in Washington, D.C. They then shared the 11.5 million documents with journalists at 109 media organizations in 76 countries, ranging from the BBC to the Miami Herald.

The combined might of those media organizations were able to scrutinize the involvement of senior figures from Argentina to Zambia.

None of them knew the source of the information.

Even Obermayer does not know who it was.

“I don’t know the name of the person or the identity of the person,” he told Wired. “But I would say I know the person. For certain periods I talked to [this person] more than to my wife.”

A few weeks before anyone named in the tranche of documents was approached, Obermayer destroyed his phone and the hard drive of the laptop he had used for the secret interactions, which were always prefaced with an old-fashioned tradecraft question like: Is it sunny? The correct answer might be: The moon is raining.

French President Hollande explicitly welcomed the massive data breach today and the British government offered a partial welcome to the trove of stolen material.

The whistleblower is unlikely to be included on the Interpol Most Wanted list anytime soon but among the world’s humiliated dictators, strongmen and some of their supposedly respectable colleagues, there’s no question who is now Public Enemy No. 1.