The Australian Signals Directorate's Australian Cyber Security Centre (ACSC) has raised concerns a number of government departments had been affected by an international software attack occurring in mid-December.

An updated alert issued by the cyber agency on Tuesday confirmed an attack against a supply chain software called SolarWinds Orion had impacted various Australian organisations and agencies.

The cyber agency urged organisations to update the software with the latest patch or isolate or disconnect it from the internet if an update is not possible.

Ongoing government contract notices show those agencies include the Department of Defence, the Department of Education, Skills and Employment, the Australian Securities and Investments Commission, Austrade and the Australian Radiation Protection and Nuclear Safety Agency.

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While the cyber agency said it hadn't received reports of any department information or data compromised, cyber security analyst Brett Callow said it was still a waiting game.

"We have no way of knowing what information was extracted [following the cyber attack]," Mr Callow said.

"I saw someone describe this in a particularly good way saying, at this point, it was about waiting for the other shoe to drop.

"And there could be a hell of a lot of shoes to drop."

Reports of the software compromise were first raised by United States cyber security firm FireEye on December 14 and is believed to have been in operation as early as March 2020.

The US Cybersecurity and Infrastructure Security Agency issued its alert and advice a week later stating a number of federal, state, and local governments had been impacted.

"This threat actor has the resources, patience, and expertise to gain access to and privileges over highly sensitive information if left unchecked," the statement read.

While the US agency did not name a specific group or country, Microsoft earlier said it suspected a nation-state capable of sophisticated techniques was behind it.

Mr Callow said it was hard to say how serious the hack was at this stage but its wide-scale nature was unprecedented and concerning.

"There really is no other incident I can think of where multiple government departments and private sector companies have potentially been compromised in one fell swoop," Mr Callow said.

"This could potentially be the most significant security incident of recent times, possibly of all time and, at this point, we simply don't know the scope of it."