On Sunday, a group of global news organizations published articles based on a trove of leaked confidential documents from a law firm in Panama. They exposed how some of the world’s most powerful people were said to have used offshore bank accounts to conceal their wealth or avoid taxes.

The documents, known as the “Panama Papers,” named international politicians, business leaders and celebrities in a web of unseemly financial transactions, according to the articles, and raised questions about corruption in the global financial system. Many of the companies and figures named in the leak have denied in the strongest terms that they had broken any laws.

What are the Panama Papers?

The Panama Papers are 11.5 million in all — or 2.6 terabytes of data — provided by an unnamed source to a German newspaper, Suddeutsche Zeitung, more than one year ago. They were taken from the files of the Panamanian law firm Mossack Fonseca, described as the fourth-largest offshore law firm in the world.

Suddeutsche Zeitung shared the data with the International Consortium of Investigative Journalists. The consortium then shared the files with reporters from 100 news organizations around the world, including The Guardian, the McClatchy newspapers, Fusion and other outlets. The New York Times did not have access to the leaked documents.

Those news media outlets are expected to publish more articles based on the Panama Papers in the coming days.

What are the most serious accusations made by the articles?

The articles said nearly 215,000 offshore shell companies and 14,153 clients were tied to Mossack Fonseca. They linked 143 politicians, their families and close associates — including 12 highly placed political leaders — to the use of tax havens to shield vast wealth.

Among those named were President Mauricio Macri of Argentina; President Petro O. Poroshenko of Ukraine; Prime Minister Sigmundur David Gunnlaugsson of Iceland; Prime Minister Nawaz Sharif of Pakistan; King Salman of Saudi Arabia; the former emir of Qatar, Hamad bin Khalifa al-Thani, and its former prime minister, Hamad bin Jassim bin Jaber al-Thani; FIFA; and the Argentine soccer star Lionel Messi, according to the consortium.

The cellist Sergei Roldugin, a close friend of President Vladimir Putin of Russia, was also named in the documents. The Guardian described Roldugin as being at the center of a $2 billion scheme “in which money from Russian state banks is hidden offshore.”

Mossack Fonseca also counted among its clients close associates of President Bashar Assad of Syria, according to the BBC, and eight current and former members of China’s Politburo. Dozens of influential donors and politicians in Britain have also been named, including Ian Cameron, the father of Prime Minister David Cameron, who ran an offshore investment fund that avoided paying taxes in the United Kingdom, according to The Guardian. The elder Cameron died in 2010.

Are any Americans named in the leaked documents?

The documents indicated that 3,500 people who owned shares in offshore companies provided the Panamanian law firm with an address in the United States, but that does not mean they are U.S. citizens. Scanned copies of at least 200 U.S. passports were included in the trove of documents, according to McClatchy, which said that many appeared to be retirees using offshore companies to buy real estate in Latin America.

In addition, almost 3,100 companies incorporated by the law firm were linked to what McClatchy called “offshore professionals” based in the United States.

But it is not clear how many United States citizens were implicated in the schemes described by the articles. So far, the documents have connected no U.S. politicians or other influential people to Massock Fonseca, according to McClatchy and Fusion.

One reason there may be relatively few Americans named in the documents is that it is fairly easy to form shell companies in the United States. James Henry, an economist and senior adviser to the Tax Justice Network, told Fusion that Americans “really don’t need to go to Panama.”

“Basically, we have an onshore haven industry in the U.S. that is as secretive as anywhere,” he said.

Do the Panama Papers show evidence of any crimes?

It is not clear. Several countries began investigations into the leaked data on Monday, including the United States, France, Germany, Australia, Austria, Sweden and the Netherlands.

Holding money in an offshore company is generally not illegal, although such financial arrangements can be used in illegal ways, for example to facilitate tax evasion or money laundering.

What has Mossack Fonseca said about the leak?

In a lengthy statement to The Guardian, the Panamanian law firm defended its practices and appeared to threaten the news agency with legal action.

The firm said that it was “legal and common for companies to establish commercial entities in different jurisdictions for a variety of legitimate reasons” and maintained that it had “always complied with international protocols” to the best of its ability to ensure that companies it incorporated were not being used for illegal or illicit purposes.

But it said the news agency had obtained “unauthorized access to proprietary documents and information taken from our company.”

“Using information/documentation unlawfully obtained is a crime, and we will not hesitate to pursue all available criminal and civil remedies,” its spokesman, Carlos Sousa, wrote.

What has been the fallout from the leak so far?

One of the first major repercussions occurred on Monday in Iceland, where residents staged a large protest outside Parliament and called for the resignation of the prime minister, Gunnlaugsson.

His name appeared in the leaked documents in connection with an offshore company he established in the British Virgin Islands with a partner, whom he later married. The leak suggested that he had sold his shares of the company to his wife for $1 just before a new law took effect that would have required him to report his ownership of it as a conflict of interest.

He said he would remain in office and maintained that he had not concealed his assets or avoided paying tax.

Many of the other figures named in the leak also have denied any wrongdoing. A spokesman for the Kremlin, Dmitri Peskov, called the Panama Papers a case of “Putinophobia” and a plot to destabilize the country. The spokesman’s wife was also named in the documents as the owner of an offshore company.