Australia's major political parties have been hit by a sophisticated cyber attack from a foreign country that also targeted the networks of federal parliament.
Liberal, Labor and National Party platforms were hacked during a breach of the Australian Parliament House network earlier this month.
"Our cyber experts believe that a sophisticated state actor is responsible for this malicious activity," Prime Minister Scott Morrison told parliament on Monday.
Security sources indicated last week China could be behind the attack, but the government's cyber security chief said the culprit was not yet clear.
There is no evidence of any attempt to interfere in Australian elections.
Still, the government has put measures in place to ensure the integrity of the electoral system.
"We have acted decisively to protect our national interests," Mr Morrison said.
ASIO boss Duncan Lewis has also been quizzed about the attack.
"I don't want to go into detail of what has been stopped and started; I am satisfied it has been managed within an inch of its life," he told a Senate committee.
"It is of core interest to me to ensure there is no foreign interference in our electoral process."
In March 2011, it was reported China was suspected of accessing the email system used by federal MPs, advisers, electorate staff and parliamentary employees.
Senate President Scott Ryan last week advised that there was no evidence that any data has been accessed, but that MPs and staff were required to change their passwords.
Labor leader Bill Shorten said the attempted hacking was of "grave concern" and came after attempted infiltration of democratic processes overseas, including in the United Kingdom and the United States.
"We cannot be complacent and, as this most recent activity reported by the prime minister indicates, we are not exempt or immune," he told parliament.
Australian Cyber Security Centre head Alastair MacGibbon said unfortunately, some of the forensic evidence which could have been useful in the investigation had been removed during action taken to stop the intrusion.
The fast action also meant agencies were not certain what information the intruder may have seen or stolen.
He said agencies always had to weigh up the risk of allowing an offender to continue versus taking fast remediation action.
"We will continue to work with our intelligence and law enforcement agencies, both here and overseas, to try to determine what they were trying to do," he told reporters in Canberra.
However, he couldn't guarantee the systems were completely hacker-free, saying given the sophistication of the attack it would be churlish to say the intruder was out and would stay out.
Australian Associated Press