A New Zealand Defence Force (NZDF) soldier alleged to be part of a far-right group arrested last December is likely to have links to overseas groups based on the charges he's facing, a security expert says.

The Linton-based soldier was arrested in December last year, and initially charged with two offences - disclosing information likely to prejudice the security or defence of New Zealand, and accessing a computer system for a dishonest purpose.

On Wednesday, several others were added - including four of espionage, two of attempted espionage, two of possession of an objectionable publication and more. 

"The big question here is whether he acted alone or this is the tip of an iceberg," security expert Paul Buchanan, director of geopolitical and strategic analysis consultancy 36th Parallel Assessments, told The AM Show on Thursday.

"The reason I say that is that militaries in other liberal democracies - the United States, the UK and Germany most recently - have found white supremacists in the ranks, actively plotting and scheming to commit terrorist acts on home soil... They've got to figure out if this fellow was just acting on his own impulses, or he's part of a larger network."

'Largely unprecedented' 

Espionage charges in New Zealand are rare.

"As far as New Zealand is concerned, to the best of my knowledge it's unprecedented in modern times," military law expert barrister Christopher Griggs told Newshub.

"The only other case I can think of in New Zealand's history was the case of Bill Sutch, who was prosecuted unsuccessfully for allegedly handing over officials secrets to the KGB in the 1970s. He was acquitted of that. As far as I know that's the only other example in modern times, so this is largely unprecedented."

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Buchanan says the espionage charges suggest the accused is either working directly for an offshore group, or the director of military prosecutions is testing whether section 78 of the Crimes Act - last updated in the early 1980s - is fit for the modern era. 

"The fellow is purported to be a member of one of these body-building white extremist groups - sort of straight-edge gone bad. The question then is, was he trying to pass information to foreign-based white supremacist groups? And if so, the espionage charge can stick. 

"But if they were purely domestic, then is this a trial of the espionage laws by a degree of separation? That is to say, given the internet, given the networking amongst white supremacist groups - including the Christchurch killer - are we going to see him put on trial not because he was passing secrets to a foreign state or a foreign actor, but he was passing it on to local actors who in turn network with foreigners?"

The group the soldier is alleged to be a part of - Wargus Christi - is New Zealand-based. White supremacists who have carried out atrocities - such as the Christchurch gunman - have been found to have international connections, through encrypted messaging apps like Telegram and no-rules websites like 8chan.

What secrets might he have been after?

Buchanan doubts the soldier would have access to top-level classified information, but may still have knowledge of sensitive information, for example troop movements in Middle East battlegrounds like Syria.

"If he was able to obtain that information about our troops' movements and pass it on to the Russians, that would be very valuable to the Russians and their allies Syria, and it wouldn't be good for our boys in the field."

Alternatively, if he was after details of local weapons caches, that would suggest intentions of a domestic terror attack.

"We're going to have to look at what exactly he was trying to obtain. That should come out during the court-martial, or it will be suppressed." 

Griggs said the NZDF has "very rigorous processes to protect classified information", calling the charges "very unusual".