A sophisticated cyber attack on Australia's federal parliamentary computer network is under investigation in a bid to find out who is behind it.
Security industry sources told AAP it was possible China could be the source of the latest breach.
There is no evidence that any data has been accessed, but the investigation is ongoing, Speaker Tony Smith and Senate President Scott Ryan said.
MPs and staff have had to change their passwords overnight on security advice.
"We have no evidence that this is an attempt to influence the outcome of parliamentary processes or to disrupt or influence electoral or political processes," they said in a joint statement on Friday.
It is understood the Australian Signals Directorate is assisting and investigating, alongside the Department of Parliamentary Services.
Australian Cyber Security Centre head Alastair MacGibbon declined to speculate on whether it was a foreign source, but admitted the breach was sophisticated.
"We of course along with our allied agencies would be very keen to understand who it is that got into the system and why," he said.
In March 2011, it was reported China was suspected of accessing the email system used by federal MPs, advisers, electorate staff and parliamentary employees.
The Australian Strategic Policy Institute's Fergus Hanson said it appears a "nation state" is behind the incident.
Prime Minister Scott Morrison said he had been briefed on the incident but there was no suggestion government departments or agencies had been the target.
Opposition Leader Bill Shorten says the breach - which he was confident was being handled properly - is a "wake up call".
"We give a lot of our data to the big international and multinational technology companies and online platforms. It's very important that we do more to protect our data."
