The red flags at the centre of AFP's suspicions about the Australian ...

Two Australian citizens, originally from Russia, have been charged with espionage after an investigation by national intelligence agencies.

Kira Korolev and her husband Igor Korolev attracted attention from authorities over trips to Russia and accessing her work laptop while on leave.

The pair were remanded in custody and will appear in court again in September.

A couple from the suburbs of Brisbane have found themselves at the centre of Russian spy allegations by Australia's intelligence agencies.

The Russian-born Australian citizens were arrested at their Everton Park home early on Friday morning over allegedly preparing espionage.

Forty-year-old Kira Korolev and Igor Korolev, 62, are accused of working together to obtain sensitive information regarding national security interests.

The extensive investigation – known as Operation BURGAZADA – has led to the Australian Defence Force (ADF) employee and her self-employed labourer husband being the first to be charged for espionage since foreign interference laws were introduced in 2018. 

This is what we know so far, and some of the red flags that captured authorities' attention. 

As an ADF private, Ms Korolev was required to report any overseas travel.

Kira Korolev is accused of obtaining Australian Defence Force material to share with Russian authorities. (Facebook)

AFP Commissioner Reece Kershaw said police would allege some of those declarations were "misleading", including "where she was allegedly at and in what country".

Matthew Sussex, adjunct associate professor at the Griffith Asia Institute, said trips to Russia would have aroused suspicion.

The trips also appear to have been taken when the federal government warned Australians against travelling to Russia.

While she was on those trips, Ms Korolev is alleged to have instructed her husband on how to log into her work account and access material to send to her.

Given she would have reported to the ADF she was out of the country, her account activity would have been a trigger.

Matthew Sussex is a senior fellow at the Centre for Defence Research at the Australian Defence College.(Supplied: ANU)

The couple had been in Australia for more than a decade before the alleged offending.

ASIO director-general Mike Burgess told reporters Australia's security clearance vetting was not foolproof — it depended on what applicants said during the vetting process.

"If you meet the requirements to get a security clearance, you will get one. But that doesn't mean to say the security journey stops at this point," he said.

Reece Kershaw and Mike Burgess address the media at a press conference.(ABC News: Nick Haggarty)

Dr Sussex said Russian spy networks often target academics and think tankers, but "the number one target is anyone with a security clearance".

"Capabilities of military kits, cyber offensive, critical infrastructure protection, and a raft of other things," Dr Sussex said.

Australia reportedly expelled a large Russian spy ring whose members were posing as diplomats last year.

"It was a network that was attempting to recruit people in the defence force with security clearance," Dr Sussex said.

Police will allege the pair sought the information with the intention to provide it to Russian authorities — whether it was actually shared is still a subject of Operation BURGAZADA's investigation.

ASIO is yet to reveal further details about how they were identified as alleged Russian assets, and what kind of information they allegedly tried to access.

And it's likely they will keep that under wraps.

"ASIO won't want to compromise its sources and methods to Russia, so we aren't likely to learn too much more, even when court proceedings commence," Dr Sussex said.

The ADF issued a statement earlier on Friday saying it was continuing to work with the Counter Foreign Interference Task-Force.

"In response to serious allegations, it is general practice to suspend an ADF member from service, including immediately cancelling the member's access to Defence bases and ICT systems," the statement said.

"As this matter is before the courts and due to personal privacy obligations, Defence will not make further comment."

Police have confirmed further charges could be laid as the investigation continues.

A more serious offence of espionage requires a direct evidential link to a foreign state, which carries penalties of 25 years to life in jail.

Right now they are facing one count each of preparing for an espionage offence, which carries a maximum penalty of 15 years' imprisonment.

Prime Minister Anthony Albanese has praised the efforts of the security agencies.

"Australia's security agencies are doing their job and they're doing it well," he told reporters. 

"People will be held to account."

The pair appeared separately in Brisbane Magistrates Court on Friday morning.

Both hearings were brief, and neither applied for bail.

They have not entered pleas.

They were remanded in custody and are due back in court on September 20.