Australia's top intelligence official says a small but concerning number of former defence insiders are putting cash before country.
ASIO boss Mike Burgess revealed in his latest annual threat assessment his agency had been tracking veterans willing to sell their military training and expertise to foreign governments for several years.
But the issue has only come to public attention recently with media reports Western pilots had been approached by China to train its military.
"These individual are lackeys - more 'top tools' than 'top guns'," Mr Burgess said.
"Selling our war-fighting skills is not different to selling our secrets - especially when the training and tactics are being transferred to countries that will use them ... against us or our allies at some time in the future."
He said in some cases former insiders had been stopped from travelling overseas to provide the training.
"But (in other cases) legal ambiguities have impeded law enforcement's ability to intervene."
He noted the overwhelming majority of veterans were Australian patriots in every sense.
"A small but concerning number are willing to put cash before country," the spy chief said.
"Third-party companies have offered Australians hundreds of thousands of dollars and other significant perks to help authoritarian regimes improve their combat skills."
He said since the announcement of AUKUS - the security cooperation deal between Australia, the US and UK - there had been a "distinct uptick in the online targeting of people working in Australia's defence industry".
"As we progress AUKUS, it's critical our allies know we can keep our secrets, and keep their secrets."
Defence Minister Richard Marles said last week he had asked his department to review its policies to stop former soldiers and personnel sharing classified information with foreign powers.
He has also flagged possible law changes.
Mr Burgess said his concerns were not limited to the defence sector.
"If we are to take security seriously, Australia needs to ensure its laws and obligations prevent former insiders transferring any form of sensitive know-how to authoritarian regimes," he said.
