The GCSB doesn't talk about how it spies on people. If it did, Kiwis would find themselves grappling with some uncomfortable truths.
"You wouldn't be able to convince a nation of people to carry around a tracking device - but they will carry mobile phones," says Paul Brislen, chief executive of the Telecommunications Users Association of New Zealand.
Each phone emits a signal which is possible to track with precision. Smartphones are even more precise, he says. "They all have GPS [global positioning system] built in."
There is room in the law to target phones with or without a warrant, whether it is to see where it is or who it is communicating with, even, if they wanted, to hear what was being said. And it is all accessible to the GCSB - even if you are a citizen or resident. In some cases, they will need a warrant. In cases in which the target is a suspected foreigner, even on New Zealand soil, no warrant is required.
Modern espionage has come a long way from the trenchcoat and alleyway. The scale and scope of sources of information have expanded hugely.
Now, it is systems like ThinThread - apparently sent to New Zealand for testing - which deliver the secrets.
Author Nicky Hager, who exposed the five-nation Echelon network in his book Secret Power, said the public faced a far greater level of intrusion now because of the scale and scope of the information. Listening to phone calls was time-consuming and likely to produce less information than sophisticated modern methods, which rely on the use of "metadata".
The term refers to "information about information" - the GCSB said two-thirds of its acts of possible illegal spying were cases in which metadata about New Zealanders was accessed.
Metadata was described by the GCSB as the sort of information found on a phone bill.
In fact, metadata describes the trails of digital footprints created by anyone in the modern world. It describes all the phone calls and text messages ever sent or made from a phone. It is every email contact point, geographical location recorded, banking transaction, bill paid or medical record transferred. Each of those will have multiple points of data and can be overlaid on dozens, hundreds or thousands of others to find links and patterns.
The result is a 3D model of a life.
ThinThread worked on metadata, creating graphs which described the huge pool of data which it analysed.
The size of the database used by the US is enormous and likely available to New Zealand, judging by a speech given by NSA whistleblower William Binney. The intelligence veteran described how he created in the 1980s a five-nation intelligence network which sounded identical to the Echelon system to which New Zealand belongs. "The whole idea was to share everything," he said.It would have been the information pool to which the GCSB surrendered Kim Dotcom's details. Court records show the bureau passed "selector" information to the Echelon/Five Eyes network featuring phone numbers, IP numbers and email addresses.
Mr Hager: "What is selector data? It is a keyword someone can search with. When you pass selector data, you are giving them a target list."