Washington DC - On Monday, the US backed by NATO and EU allies condemned a series of cyberattacks allegedly carried out at the behest of the Chinese state, in particular the hacking of Microsoft Exchange servers earlier this year.

The attacks enabled hackers to gain access to computer networks around the world via the Microsoft servers, and are estimated to have affected over a quarter of a million servers worldwide.

Most of the victims were in the private sector, according to a statement by Secretary of State Antony Blinken.

China's Ministry of State Security "has fostered an ecosystem of criminal contract hackers who carry out both state-sponsored activities and cybercrime for their own financial gain," the statement said.

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NATO, Britain, Canada, Australia, and the European Union also issued statements over the Microsoft Exchange Server hack.

The EU, which imposed its first-ever sanctions for cybercrime on China and Russia last year, said the incident had "undermined the security and integrity of thousands of computers and networks worldwide."

Hackers continue to exploit the access gained to date, EU foreign affairs chief Josep Borrell said.

"The Australian Government is also seriously concerned about reports from our international partners that China's Ministry of State Security is engaging contract hackers who have carried out cyber-enabled intellectual property theft for personal gain and to provide commercial advantage to the Chinese Government," a statement from the country's government added.

The charges could set Washington and Brussels on further confrontation course with China.

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President Joe Biden has been pushing a tough course against China since he took office. The Biden administration imposed sanctions against Russia in the past because of hacker attacks.

The Justice Department on Monday announced charges against four Chinese nationals, three of them government agents, for the alleged state-backed hacking campaign.

They are accused of having stolen intellectual property in a range of sectors: from commercial aviation, a US defense contractor, a Swiss chemicals company, universities, to medical research, over several years.

China has rejected the cyberattack allegations by the United States and its NATO and EU allies, calling them "slander."

The accusations were unfounded and made for purely political reasons, Chinese Foreign Ministry spokesperson Zhao Lijian said on Tuesday.

China is strictly against any form of cyberattacks, and neither supports nor tolerates them, he added. The spokesperson accused the US of being "the biggest source of cyberattacks worldwide."

The US government and its allies have not yet announced any sanctions against China.