National security agencies are continuing to scour the Parliament's computer network for threats to MPs' data after what is being described as a "sophisticated" hack attack that could be the work of a foreign government.

Alastair MacGibbon, head of the Australian Cyber Security Centre, said the government's cyber experts would work over coming days and weeks to make sure all the breaches had been detected and the hackers' presence removed.

The hacking comes just three months ahead of the federal election, prompting fears that if MPs emails or data were stolen they could be used to cause political interference of the style Russia perpetrated against the United States in the 2016 presidential campaign.

Sources said the fact that Parliament had significantly upgraded its cyber defences since an attack by Chinese intelligence agencies in 2011 suggested the latest hackers were highly skilled, potentially pointing to a foreign government.

Mr MacGibbon stressed it was too early to say who was behind the attack but said this part of the investigation.

He said the main concern was to “get the offender out of the system and keep them out of the system”.

"You might know of some of their entry points and some of the ways they’ve grafted themselves into a system and you can take action against those and do things like the password reset," he said.

Federal Parliament's computer system has been hacked, potentially exposing MPs' data. Graham Tidy

"We just need to be rational in knowing that they may have other entry points and other places that they have code hidden inside the network. So we’ll work over coming days and weeks with the Department of Parliamentary Services … to protect the system so politicians and their staff can go about their business working for Australians."

The Australian Signals Directorate, the government's key agency on cyber-security, moved swiftly in recent days to lock down and protect the network. Mr MacGibbon refused to say how long the hackers might have been in the network before they were detected.

All MPs, including ministers, use the parliamentary network. House Speaker Tony Smith and Senate President Scott Ryan said in a joint statement there was "no evidence that any data has been accessed or taken at this time, however this will remain subject to ongoing investigation".

They said they had no evidence the hack was an effort to "influence the outcome of parliamentary processes or to disrupt or influence electoral or political processes".

Mr MacGibbon declined to comment on whether the attack might be part of a Russian-style foreign interference campaign, pointing to Mr Smith and Senator Ryan's statement.

China has been responsible for several previous high-profile hacks on Australian government systems, including breaching Parliament’s computer network in 2011, which may have allowed Chinese spies to read the emails of MPs and their staff for months.

Fergus Hanson, a cyber expert with the Australian Strategic Policy Institute, said any data such as emails that were stolen could be used in various ways to wreak havoc with Australian democracy.

“It could be used to target one particular party … or used to discredit public institutions, to show that the Parliament may not be functioning the way we think it should be, and to undermine public trust,” he said.

“This is a great system to be targetting if you are a nation-state. Lots of juicy correspondence between staffers about who is doing what and dirt files on politicians.”

Mr Smith and Senator Ryan said that out of an "abundance of caution", user passwords had been reset.