A mystery hacker has stolen information about Australia's warplanes from a defence subcontractor.
About 30 gigabytes of data was stolen, including information on Australia's $17 billion Joint Strike Fighter program, and $4 billion P-8 surveillance aircraft project.
As first reported by ZDNet, the malicious actor infiltrated the system last July and authorities were only alerted in November 2016.
Experts at the Australian Signals Directorate (ASD) codenamed the hacker "Alf" after the character from the television drama Home and Away.
The ASD officials started fixing the system in December and referred to the period before they responded as "Alf's Mystery Happy Fun Time".
The 50-person aerospace engineering firm subcontracts to the Defence Department and had one person managing its IT functions for about 50 staff.
Data on the F-35 Joint Strike Fighter, P-8 Poseidon surveillance aircraft and C-130 transport plane was stolen.
The Federal Government on Wednesday night emphasised the information was commercially sensitive, but not classified.
"Today, while presenting at a conference in Sydney, an ASD official disclosed information about the theft of data from an Australian company," a spokesman for the Australian Cyber Security Centre said.
"While the Australian company is a national security-linked contractor and the information disclosed was commercially sensitive, it was unclassified.
"The Government does not intend to discuss further the details of this cyber incident."
The minister responsible for cyber security, Dan Tehan, earlier this week announced the breach, without providing details.
Mr Tehan said it was unclear who launched the incursion, but the Government was not ruling out a foreign government.
"It could have been a state actor, it could have been cyber criminals, and that's why it was taken so seriously," he said.