Australian Prime Minister Julia Gillard's parliamentary computer and the foreign and defence ministers' machines are all suspected of being hacked, with China under suspicion, reports said Tuesday.
Sydney's Daily Telegraph said American intelligence officials tipped off the government that several thousand emails may have been accessed from the computers of at least 10 ministers.
As well as Gillard, they reportedly included Foreign Minister Kevin Rudd and Defence Minister Stephen Smith.
The paper said the espionage occurred over more than a month, beginning in February.
"Four separate government sources confirmed that they had been told Chinese intelligence agencies were among a list of foreign hackers that are under suspicion," it said.
One of the sources said the revelations were "deeply concerning".
"These claims need to be examined seriously," they said.
Security experts cited by another News Limited newspaper, The Australian, said they believed the hackers may have been looking for clues on government attitudes to major resource projects.
Intelligent Risk chief executive Neil Fergus said interest in Australian commercial secrets may have prompted the attacks.
"There are massive resources projects on the drawing board in Australia, they loom very large in the thinking of a number of other countries," he said.
"Whether we green-light projects is of critical importance. I would not understate the possibility of that, given Australia's resources boom and its importance to a number of our key trading partners."
Attorney-General Robert McClelland refused to confirm or deny the incident.
"It's the long standing practice of successive Australian governments not to comment on the operations of security and intelligence agencies," he said in a statement.
"Australia's security and intelligence agencies, as a matter of course, work closely and co-operatively with their international counterparts on cyber security.
"The Australian government takes the issue of cyber security very seriously and is constantly strengthening cyber security measures," he said.
Gillard similarly refused to comment when asked by reporters in Perth.
"We don't comment on intelligence matters," she said.
China, meanwhile, denied the claims. "Any accusations against the Chinese government are believed to be groundless and made out of ulterior purposes," foreign ministry spokeswoman Jiang Yu told reporters.
The cyber attacks are believed to have been on the Australian Parliament House email network, the less secure of two networks used by MPs.
Ministers use a departmental network for more high-security communications.
A report from the Australian National Audit Office, meanwhile, said more than 10 percent of passwords used in Gillard's department could be easily broken in an hour by hackers using "brute force".
It said passwords needed to be more complex and access to web-based email accounts such as Hotmail and Gmail should be blocked.
Basic software updating was not being done regularly enough and this left security holes, the audit found.
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