Australia's main political parties and parliament were hit by a "malicious intrusion" on their computer networks, Prime Minister Scott Morrison said.
The cyber-attack revealed two weeks ago was carried out by a "sophisticated state actor", he said.
But he added there was "no evidence of any electoral interference". The nation will hold an election within months.
The attack being investigated was at first thought to involve only the parliament's servers.
"During the course of this work, we also became aware that the networks of some political parties - Liberal, Labor and Nationals - have also been affected," Mr Morrison told the House of Representatives on Monday.