FRANKFURT, Germany — A group of investigative journalists on Monday published the names of thousands of offshore companies at the heart of a massive trove of data on the finances of the rich and powerful that has become known as the Panama Papers.

The information contains basic corporate information about companies, trusts and foundations set up in 21 jurisdictions including Hong Kong and the U.S. state of Nevada. The data was obtained from Panamanian law firm Mossack Fonseca, which said it was hacked.

Users can search the data and see the networks involving the offshore companies, including, where available, Mossack Fonseca’s internal records of the true owners.

Information and documents on bank accounts, phone numbers and emails have been removed from the database.

Mossack Fonseca said last week it had sent a cease and desist letter to the ICIJ urging the organization not to publish the database, “taking into consideration that it is based on the theft of confidential information.”

The ICIJ said it was putting the information online “in the public interest” as “a careful release of basic corporate information,” not a “data dump,” as it builds on an earlier database of offshore entities.

Setting up an offshore company is not by itself illegal or evidence of illegal conduct, and Mossack Fonseca said it observed rules requiring it to identify its clients.

The ICIJ prefaced the database release by noting that the appearance of particular persons and companies on the list doesn’t imply wrongdoing.

But anti-poverty campaigners say shell companies can be used by the wealthy and powerful to shield money from taxation, or to launder the gains from bribery, embezzlement and other forms of corruption. The Group of 20 most powerful economies has agreed that individual governments should make sure authorities can tell who really owns legally registered companies, but implementation in national law has lagged.

Reports based on the documents quickly led to the resignation of Iceland’s Prime Minister David Gunnlaugson after it was revealed he and his wife had set up a company in the British Virgin Islands that had holdings in Iceland’s failed banks. British Prime Minister David Cameron, who had campaigned for financial transparency, faced questions about shares he once held in an offshore trust set up by his father. The ICIJ reported that associates of Russian President Vladimir Putin moved some $2 billion through such companies. Putin’s spokesman dismissed the report.

The ICIJ said Monday that Mossack Fonseca had files on dozens of Americans who have faced accusations of civil or criminal financial misconduct. The people who had set up offshore companies included people with publicly available records of their legal troubles.