A day after US formally accused China of carrying out a massive Microsoft hack in March, Beijing on Tuesday China sharply denied the allegations, reports AFP. China said Washington was the “world champion” of cyber attacks. It also condemned American allies for signing up to a rare joint statement of condemnation. The United States has also charged four Chinese nationals over the “malicious” hack in March.

US Secretary of State Antony Blinken said the attack on Microsoft Exchange, a top email server for corporations around the world, was part of a “pattern of irresponsible, disruptive and destabilizing behaviour in cyberspace, which poses a major threat to our economic and national security.”

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Blinken added that China’s Ministry of State Security “has fostered an ecosystem of criminal contract hackers” and they carry out both state-sponsored activities and cybercrime.

According to US Department of Justice, four Chinese nationals had been charged with hacking the computers of dozens of companies, universities and government bodies in the United States and abroad between 2011 and 2018.

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Meanwhile, US President Joe Biden told reporters that they were the investigation was still going on. “The Chinese government, not unlike the Russian government, is not doing this themselves, but are protecting those who are doing it, and maybe even accommodating them being able to do it,” Biden told reporters.

In a step the Biden administration hailed as unprecedented, the United States coordinated its statement Monday with allies — the European Union, Britain, Australia, Canada, New Zealand, Japan and NATO.

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The Microsoft hack, which exploited flaws in the Microsoft Exchange service, affected at least 30,000 US organisations including local governments as well as organisations worldwide.

Accusations of cyberattacks against the United States have recently focused on Russia, rather than China. The US officials say that many of the attacks originate in Russia, although they have debated to what extent there is state involvement. Russia denies responsibility.

This year has seen a slew of prominent ransomware strikes that have disrupted a major US pipeline, a meat processor and the software firm Kaseya, which affected 1,500 businesses. Last week, Washington offered $10 million for information about foreign online extortionists.