What’s the deal with the massive Panama Papers data leak?

A data breach at Panamanian law firm Mossack Fonseca is being touted as the largest ever, at least in terms of the sheer volume of information leaked.

The leaked information allegedly details the ways dozens of high-ranking politicians, their relatives or close associates in more than 40 countries, including the U.K., France, Russia, China, and India, have used offshore companies to hide income and avoid paying taxes. Starting on Sunday, more than 100 news organizations filed reports based on the leaked information.

The numbers: The leaks reportedly cover 11.5 million confidential documents dating from the 1970s through late 2015. The 2.6 terabytes of leaked data include 4.8 million emails, 3 million database format files, 2.2 million PDFs, 1.1 million images, and 320,000 text documents.

How did the leak happen? Details are sketchy, but a representative of Mossack Fonseca has confirmed news reports saying the leak stems from an email hack. It’s unclear how the email attack happened, but tests run by outside security researchers suggest Mossack Fonseca did not encrypt its emails with Transport Layer Security protocols.

An email server attack could have happened in “multiple ways,” said Zak Maples, a senior security consultant at MWR InfoSecurity, a cybersecurity consultancy. It appears that the server itself was compromised instead of individual mailboxes brute-forced in password-guessing attacks, because of the volume of data compromised, he said by email.

“This breach is quite possibly a broader compromise of the organization,” Maples added. “Attackers may have compromised the Mossack Fonseca network and elevated privileges to that of a domain administrator or email administrator and used these elevated privileges to access and download all the data contained on the e-mail server.”

Who is the leaker? The source is unknown, likely even to the news organizations using the leaked information. The leaker reportedly communicated through encrypted chat and email.

The firm’s response: Mossack Fonseca has denied wrongdoing, saying it has only assisted clients in setting up legitimate companies.”While we may have been the victim of a data breach, nothing in this illegally obtained cache of documents suggests we’ve done anything wrong or illegal, and that’s very much in keeping with the global reputation we’ve worked hard to build over the past 40 years of doing business the right way,” the company said in a statement. “Obviously, no one likes to have their property stolen, and we intend to do whatever we can to ensure the guilty parties are brought to justice.”