Concern over an imminent terrorist act led our internal intelligence agency to carry out urgent surveillance without a legal warrant under special new powers.
It is unclear whether the suspected terrorist activity was aimed inside New Zealand or offshore.
The fact was revealed in a sparse report from Security Intelligence Service director Rebecca Kitteridge made public this week.
It reveals only that she exercised her powers to authorise spying in New Zealand without a warrant for a 24-hour period.
Under law, which has been in force since December 2014, the maximum time period the power can be exercised is 24 hours.
The report from Ms Kitteridge also shows that the SIS followed up its urgent surveillance with an application for a warrant "in relation to the same subject matter", continuing the intelligence operation.
Ms Kitteridge was compelled to make public the warrantless surveillance as part of the disclosure requirements included in the law change.
It also requires the Inspector General of Intelligence and Security - currently Cheryl Gwyn - investigate the use of the power to make sure it was appropriate.
The law change shows the broad conditions under which the SIS director could use the power to carry out warrantless surveillance. It states that the use of the power can only come after the director is satisfied it is needed for the "detection, investigation or prevention of any actual, potential or suspected terrorist act or facilitation of a terrorist act".
It raises the questions over who - or what - was such a threat that Security Intelligence Service director Rebecca Kitteridge needed to exercise the emergency powers.
Former CIA contractor and intelligence expert Dr Paul Buchanan said the Herald's publication last year of a supposed ISIS sympathiser could have been the spur for the warrantless surveillance.
The sudden propulsion of the man into the media, holding forth on views which favoured ISIS, would have alarmed the security services, said Dr Buchanan.
"They don't have the luxury of assuming the best or saying 'we'll hold back and wait'. Once things get to a certain level, they have to act."
The Herald reported on Harun Abdul-Majeed SaifuAllah, who had posted a picture of himself on Facebook holding an AK47-style rifle and an ISIS flag, which he later claimed was an Airsoft replica.
In an interview with the Herald, Mr SaifuAllah said he supported Islamic State because "I support what they do".
He told the Herald he had been the focus of SIS attention and it was repeated questions about his interest in ISIS which had radicalised him. He said it was SIS interest which "made me look into it even more and these people are to blame for some of the views that I have".
Mr SaifuAllah said there was network of young men in New Zealand with the same views.
"People are waking up...it's not like getting together in one big terrorist hub or anything but people are just understanding the reality."
In the interview, Mr SaifuAllah said a terror attack in New New Zealand would not benefit IS, he said he did see a problem in other countries.
"There's a reason these countries are being hit it's because they are full on in the campaign against then."
Green Party co-leader Metiria Turei called on Security Minister Chris Finlayson to tell the public the context in which the warrantless surveillance was carried out.
She said there was such a focus on - and concerns around - ISIS that the public would benefit from knowing whether this incident was one with links to the group.
Ms Turei said the declaration of the use of warrantless surveillance powers showed improved focus on the law by the SIS. "It's good to see the SIS is finally following the law."
Herald attempts to contact Mr SaifuAllah were unsuccessful. The interest Mr SaifuAllah said the SIS held in his activities shows he likely would have figured on its "watch list" of 40 people, which the Herald understands is determined by risk but also the service's ability to watch people.
Those of lesser concern would figure lower on the list and be subject to far less regular or rigorous checks than those high on the list.
The public emergence of a figure on the list with what appeared to be an AK47 would likely have created a sense of urgency for more information about the individual.