Australian intelligence agencies reportedly found China was responsible for a cyber attack on Federal Parliament earlier this year, but kept the finding secret to avoid souring trade relations with Beijing.
News agency Reuters reported on Monday the Australian Signals Directorate (ASD) found in March that China's Ministry of State Security was responsible for a "sophisticated" hack attack on MPs' emails and the networks of the Australian Labor Party, the Liberals and the Nationals.
It prompted fears at the time that if MPs' emails or data were stolen, they could be used to cause political interference during the May election campaign of the kind Russia perpetrated against the United States in the 2016 presidential campaign.
Reuters cited five sources who had declined to be identified because of the sensitivity of the issue.
Australian authorities felt there was a "very real prospect of damaging the economy" if it were to publicly accuse China over the attack, it reported.
The Morrison government declined to comment on Monday. It has not disclosed who it believes was behind the attack or any details of the ASD report.
The report comes amid a frosty relationship between Canberra and Beijing over the US-China trade conflict and China's military expansion in the South China Sea and growing influence in the Pacific.
At the time the hacks came to light in February, Prime Minister Scott Morrison said security agencies had detected the activity and acted "decisively to confront it". He told Parliament he would not "go into the detail of these operational matters" but that experts believed a "sophisticated state actor is responsible for this malicious activity".
The attack on the political parties gave the hackers access to private email correspondence between politicians, public servants, staff and other citizens, two sources told Reuters.
House of Representatives Speaker Tony Smith and Senate President Scott Ryan said in a joint statement at the time there was "no evidence that any data has been accessed or taken at this time, however, this will remain subject to ongoing investigation".
China's Foreign Ministry has continued to deny any involvement in the cyber attack.
"When investigating and determining the nature of online incidents, there must be full proof of the facts, otherwise it's just creating rumours and smearing others, pinning labels on people indiscriminately," the ministry said in a statement sent to Reuters.
"China hopes that Australia can meet China halfway, and do more to benefit mutual trust and co-operation between the two countries."
- SMH/The Age