Australia is looking into claims China tried to poach ex-military personnel to train its forces.
Defence Minister Richard Marles has launched an urgent investigation, saying there's enough evidence to warrant a review of defence policies and procedures.
The defence department began a preliminary investigation last month after reports China approached former personnel to provide military training.
"For those who do come into possession of our nation's secrets ... there is an enduring obligation to maintain those secrets for as long as they are secrets," he told reporters on Wednesday.
"It's really important we have the most robust framework possible in place to protect Australia's information and protect our secrets."
Mr Marles says any weaknesses will be plugged.
The defence minister did not confirm how many people were being investigated, except to say his department was investigating "a number of cases".
"It's no secret that defence activities, people and assets are targets for foreign intelligence services," he said.
Mr Marles would not confirm if a specific incident had sparked the investigations.
The department will report back to the minister by December 14.
Opposition defence spokesperson Andrew Hastie branded the revelations concerning and welcomed the review.
"Our national military secrets, including tactics, techniques and procedures for our elite fighter pilots, must be safeguarded by serving defence members and our veterans," he said.
"They are not for sale to another country."
He said the opposition would work with the government on urgent legislation to plug any gaps.
Defence's deputy security secretary told parliamentarians Australian military personnel were "attractive targets".
"The onus is on us ... to support them and build really deep awareness in our community that foreign actors will target our people for their unique skills," Celia Perkins told a Senate estimates hearing.
Liberal senator James Paterson asked defence bureaucrats whether personnel had taken up an offer from a South African intermediary but they declined to provide further detail.
RAAF chief Robert Chipman said any unauthorised disclosure was an offence and that was understood by service personnel.
"There is no doubt the training they undertake will include sensitive information they are obligated to protect," he said.
"It's clear to them they are required to protect that information while they are in the service and once they have left."
But Liberal MP and former commando Keith Wolahan said military laws may not be completely understood by personnel and any law reform also needed to factor in education.
"The best law enforcement is prevention," he told the ABC.
Mr Hastie said defence personnel had a moral obligation to the nation during and after their service.
"Money is a great enticement and when people get an offer they can't refuse, sometimes they take it up," he said.
A former United States military pilot was arrested in Orange at the start of the month.
Daniel Duggan is facing extradition to the US after arriving from China and interacting with Australian intelligence agencies.
The former US citizen and ex-marines pilot had been working in China as an aviation consultant since 2014.
Details of Washington's arrest warrant and charges are sealed.