The United States and a coalition of allies have accused China of a global cyber hacking campaign that employed contract hackers, specifically attributing a large Microsoft attack disclosed earlier this year to actors working on the country's behalf.
Opening a new area of tensions with China, the United States is joined by NATO, the European Union, the United Kingdom, Australia, Japan, New Zealand and Canada to level the allegations.
"The United States and countries around the world are holding the People's Republic of China accountable for its pattern of irresponsible, disruptive, and destabilising behaviour in cyberspace, which poses a major threat to our economic and national security," US Secretary of State Anthony Blinken said in a statement on Monday.
Also on Monday, the US Justice Department said four Chinese citizens - three security officials and one contract hacker - were charged in a global hacking campaign aimed at dozens of companies, universities and government agencies in the United States and abroad.
The activities took place between 2011 and 2018 that focused on information that would significantly benefit Chinese companies and businesses, it said.
The opening of a new front in the governments' war against hacking comes a month after G7 and NATO leaders agreed with US President Joe Biden at summits in Cornwall, England, and Brussels in accusing the Chinese government of posing systemic challenges to the world order.
The governments formally attributed intrusions exploiting vulnerabilities in the Microsoft Exchange Server that were disclosed in March "cyber actors affiliated with" China's Ministry of State Security, Blinken said.
The Chinese embassy in Washington DC did not immediately respond to a request for comment.
Chinese officials have previously said China is also a victim of hacking and opposes all forms of cyber attacks.
US officials said the scope and scale of hacking attributed to China has surprised them, along with China's use of "criminal contract hackers".
"The PRC's Ministry of State Security (MSS) has fostered an ecosystem of criminal contract hackers who carry out both state-sponsored activities and cybercrime for their own financial gain," Blinken said.
US security and intelligence agencies will outline more than 50 techniques and procedures that "China state-sponsored actors" use in targeting US networks, a senior administration official said.
Chinese state-sponsored cyber actors consistently scan target networks for critical and high vulnerabilities within days of the vulnerability's public disclosure, the 31-page US cybersecurity advisory seen by Reuters says.
The United States in recent months has focused heavy attention on Russia in accusing Russian cyberhackers of a string of ransomware attacks in the United States.
In Monday's announcement, US officials formally blamed the Chinese government "with high confidence" for the hack that hit businesses and government agencies in the United States using a Microsoft email service.
Microsoft has already accused Chinese authorities of responsibility.
The operation specifically exploited weaknesses in Microsoft's exchange program, a common email software.
Cybersecurity experts were shaken by the scale and volume of the incident, totalling thousands of potential US victims.
The senior Biden administration official said US concerns about Chinese cyber activities have been raised with senior Chinese officials.
"We're not ruling out further action to hold the PRC accountable," the official said.
Blinken cited the Justice Department indictment of the three Chinese security officers and a contract hacker as an example of how the United States will impose consequences.
The defendants and officials in the Hainan State Security Department, a regional state security office, tried to hide the Chinese government's role in the information theft by using a front company, according to the indictment, which was returned in May and unsealed Friday.
The campaign targeted trade secrets in industries including aviation, defence, education, government, health care, biopharmaceutical and maritime industries, the Justice Department statement said.
Victims were in Austria, Cambodia, Canada, Germany, Indonesia, Malaysia, Norway, Saudi Arabia, South Africa, Switzerland, the United Kingdom and the United States.
Australian Associated Press