It would have taken a high threat to national security to trigger the Security Intelligence Service to carry out surveillance without a warrant, a security analyst says.
Paul Buchanan from 36th Parallel Assessments said he hoped the SIS only carried out surveillance without a warrant because they had real-time immediate information about activities that were a high risk to national security.
"One would hope that this was in fact a real concern of theirs, and I only say that because the track record of the SIS in the past has been rather sketchy when it comes to ascertaining threat," he said.
New powers were granted to the agency in a 2014 anti-terror law change allowing surveillance without a warrant.
SIS director Rebecca Kitteridge reported in the agency's annual review that one authorisation was granted between July and December last year.
Minister in charge of the SIS Chris Finlayson would not confirm the circumstances that led to the authorisation, but said the use of warrantless surveillance was pretty rare, issued in urgent or emergency situations.
Mr Buchanan said because the SIS had not dropped the investigation, instead going on to secure an intelligence warrant, it could be assumed the surveillance had continued and the agency was not following a false lead.