Australia has joined the US and other allies in accusing China of masterminding a global hacking campaign using contract criminals.
Australia's foreign affairs, home affairs and defence ministers say China's Ministry of State Security exploited vulnerabilities in Microsoft Exchange software that affected thousands of networks worldwide.
The federal government has joined the US, UK, European Union, Japan, New Zealand and NATO - the North Atlantic Treaty Organisation - in levelling the accusations.
Australia's Home Affairs Minister Karen Andrews says the hacks opened the door for cyber criminals to exploit the private sector for illicit gain.
Businesses and organisations, rather than individuals, were the main hacking targets in Australia in January.
"It was a significant data breach and access was enabled to the systems so that they could be commanded and controlled outside the organisation," the home affairs minister told reporters on Tuesday.
Australia has in the past avoided publicly attributing cyber attacks to China, but believes it's in the national interest to do so right now.
Defence Minister Peter Dutton said China was sponsoring hackers to "hoover up" intelligence and intellectual property.
"This is a worldwide attempt to expose what China is up to online and it's regrettable they are keeping the company of countries like North Korea, Russia and Iran," he said.
But the minister maintained Australia could still have a trading relationship with China while calling out such action.
Meanwhile, US authorities charged three Chinese security officials and one contractor with hacking between 2011 and 2018.
A front company was set up to obfuscate the Chinese government's role in the campaign to steal trade secrets and confidential business information worldwide, US officials said.
Former Australian cyber security adviser Alastair MacGibbon warned China was unlikely to face significant consequences for working with criminals.
"China has used contractors to carry out what you would suggest is a legitimate state-based espionage activity," he said.
"We may not like it but it's kind of what nations do to each other.
"And those contractors have then, for their own gain, carried out activities in parallel to what they were doing for the Chinese government."
Assistant defence minister Andrew Hastie said cyberspace was the latest global battlefield.
Cyber crime more broadly cost Australia's economy about $3.5 billion in 2019.
In the last financial year, business email compromise had affected more than 4500 organisations and cost them upwards of $80 million.
China's embassy said it opposed cyber attacks and theft.
Its spokesperson also rejected Australia's "groundless accusations" and said the country was being hypocritical, "like a thief crying 'stop the thief'".