The Biden administration and its allies has formally accused China of the mass-hacking of Microsoft Exchange servers earlier this year, which prompted the FBI to intervene as concerns rose that the hacks could lead to widespread destruction.

The mass-hacking campaign targeted Microsoft Exchange email servers with four previously undiscovered vulnerabilities that allowed the hackers — which Microsoft already attributed to a China-backed group of hackers called Hafnium — to steal email mailboxes and address books from tens of thousands of organizations around the United States.

Microsoft released patches to fix the vulnerabilities, but the patches did not remove any backdoor code left behind by the hackers that might be used again for easy access to a hacked server. That prompted the FBI to secure a first-of-its-kind court order to effectively hack into the remaining hundreds of U.S.-based Exchange servers to remove the backdoor code. Computer incident response teams in countries around the world responded similarly by trying to notify organizations in their countries that were also affected by the attack.

In a statement out Monday, the Biden administration said the attack, launched by hackers backed by China’s Ministry of State Security, resulted in “significant remediation costs for its mostly private sector victims.”

“We have raised our concerns about both this incident and the [People’s Republic of China’s] broader malicious cyber activity with senior PRC Government officials, making clear that the PRC’s actions threaten security, confidence, and stability in cyberspace,” the statement read.

The National Security Agency also released details of the attacks to help network defenders identify potential routes of compromise.

Several allies, including the U.K. and the members of NATO, also backed the Biden administration in its findings. In a statement, the U.K. government found Beijing responsible for a “pervasive pattern” of hacking. The Chinese government has repeatedly denied claims of state-backed or sponsored hacking.

The Biden administration also blamed China’s Ministry of State Security for contracting with criminal hackers to conduct unsanctioned operations, like ransomware attacks, “for their own personal profit.” The government said it was aware that China-backed hackers have demanded millions of dollars in ransom demands against hacked companies. Last year, the Justice Department charged two Chinese spies for their role in a global hacking campaign that saw prosecutors accuse the hackers of operating for personal gain.

Although the U.S. has publicly engaged the Kremlin to try to stop giving ransomware gangs safe harbor from operating from within Russia’s borders, the U.S. has not previously accused Beijing of launching or being involved with ransomware attacks.

“The PRC’s unwillingness to address criminal activity by contract hackers harms governments, businesses, and critical infrastructure operators through billions of dollars in lost intellectual property, proprietary information, ransom payments, and mitigation efforts,” said Monday’s statement.

The statement also said that the China-backed hackers engaged in extortion and cryptojacking, a way of forcing a computer to run code that uses its computing resources to mine cryptocurrency, for financial gain.

The Justice Department also announced fresh charges against four China-backed hackers working for the Ministry of State Security, which U.S. prosecutors said were engaged in efforts to steal intellectual property and infectious disease research into Ebola, HIV and AIDS, and MERS against victims based in the U.S., Norway, Switzerland and the United Kingdom by using a front company to hide their operations.

“The breadth and duration of China’s hacking campaigns, including these efforts targeting a dozen countries across sectors ranging from healthcare and biomedical research to aviation and defense, remind us that no country or industry is safe. Today’s international condemnation shows that the world wants fair rules, where countries invest in innovation, not theft,” said deputy attorney general Lisa Monaco.