A highly sensitive military database containing the personal details of tens of thousands of Australian Defence Force (ADF) members was shut down for 10 days due to fears it had been hacked.

Key points: Defence Force recruitment records are maintained by an outsourced company

Defence Force recruitment records are maintained by an outsourced company Its network was shut down in February amid fears the information had been compromised

Its network was shut down in February amid fears the information had been compromised Former soldiers turned politicians have demanded more answers about the incident

The ABC can reveal Defence Force Recruiting's outsourced electronic records system was taken offline and quarantined from other military networks in February, while IT specialists worked to contain an apparent security breach.

Since 2003, the Powerforce database has stored sensitive information about ADF recruits, under a contract awarded to the ManpowerGroup company.

Details stored on the online system include medical exams, psychological records and summaries of initial interviews with potential recruits.

The Defence Department acknowledged a "potential security concern" but suggested an investigation found there was no evidence of data being stolen.

"The security of information systems and personnel data is of paramount importance to Defence," a spokesman said in a statement.

"Due to a potential security concern, some elements of the Defence Force Recruiting Network (DFRN) were proactively taken offline on February 2, 2020. Normal operation resumed on February 12, 2020.

"An investigation did not identify any evidence to suggest a compromise of information had occurred."

A source familiar with the investigation said the "security concern" was detected before Christmas and sparked fears within Defence that hackers may have accessed the DFRN.

"Over the summer holidays, crisis meetings were held twice a day to deal with the situation," a Defence insider told the ABC, speaking on the condition of anonymity.

"During this period, email contact between Defence Force Recruiting and computers connected to the Defence Department's protected network was suspended."

Soldiers-turned-politicians demand answers

Former SAS captain Andrew Hastie said no breach could be considered small. ( ABC News: Marco Catalano )

Liberal MP Andrew Hastie is among tens of thousands of serving ADF members and veterans whose personal details are stored in the Powerforce database.

The former SAS captain and chairman of Parliament's Intelligence Committee described the potential database breach as a "very concerning development".

"Our government and defence networks should be fortresses — no breach can be considered small," the Liberal MP said.

"For Defence to take this offline for 10 days suggests a fairly sophisticated actor."

His concerns are shared by Labor backbencher and former commando Luke Gosling, who is demanding more answers about the possible hack.

"A whole range of information that we wouldn't want to go into the wrong hands — the Federal Government needs to let us know what's happened," he said.

"There needs to be a thorough investigation into this."

ManpowerGroup Australia said it was "aware of a potential issue identified with the Defence Force Recruiting Network (DFRN), requiring Defence to proactively take elements of this network offline".

"All elements of the DFRN have since been restored to full operations," a spokesperson told the ABC.

Last year, Minister for Defence Personnel Darren Chester announced a two-year extension to the recruiting services contract with ManpowerGroup.

Defence a regular target for foreign hackers

Revelations of a possible breach of the Defence Force Recruiting Network follows confirmation that a "sophisticated actor" had accessed student data from the Australian National University in 2018.

Defence insiders have blamed China for the massive hacking operation, which included records of numerous military personnel who had studied at the ANU's National Security College.

In 2017, cyber thieves hacked into the computer system of a national security contractor, stealing large amounts of the defence suppliers' data.

Details of the multi-billion-dollar Joint-Strike Fighter and P-8 Surveillance plane programs were among information stolen from an Adelaide-based defence subcontractor by hackers.

Intelligence gathering by the Australian Signals Directorate was involved in forensic analysis of the attack and it was alerted a hacker had been inside the subcontractor's computer system for five months.

The ASD investigators codenamed the hacker "Alf" after the Alf Stewart character from the Australian TV program Home and Away.

It was not hard to crack the password in that case, the system's username was "admin admin" and the password was "guest guest".

In 2016, Four Corners revealed the Defence research division had been breached by hackers.

Intelligence sources said they suspected the hackers in the cases were sponsored by Beijing.

At the time, the Prime Minister's then cyber security adviser Alistair MacGibbon said the Australian Government was "attacked on a daily basis".