Kiwis who deal with organisations that get cyber protection from the GCSB have been told there are strict controls around the use of their data.
A growing number of private companies and government departments are getting official protection from powerful cyber attacks.
A telecommunications firm, a major IT company and officials in a key government department have all been hit in recent months.
Yesterday, acting GCSB director Una Jagose revealed new details about its Cortex cyber security program, which is designed to counter attacks too strong for commercial software.
She had been due to give the talk earlier this month but it was scuppered after protesters unfurled a banner labelling it a propaganda exercise.
The office of Privacy Commissioner John Edwards, which hosted yesterday's event in Wellington, asked guests not to publicise the time or location beforehand.
Ms Jagose's speech reflects a marked increase in public relations efforts by the country's intelligence agencies.
A major review of the GCSB and NZSIS is under way after a series of revelations and allegations, including illegal spying in the Kim Dotcom case.
Rebecca Kitteridge, NZSIS director, recently said a reality TV show similar to Border Patrol would show Kiwis they had nothing to fear from her agency, and Ms Jagose made a similar statement yesterday.
"There is a thorough vetting that is required ... people agree to a full review of their financial background, what they do in their spare time, their personal relationships, their online habits, any other habits.
"As a result, our people have very high levels of integrity and loyalty."
While Cortex is mostly automated, some of those staff work with less than 0.005 per cent of all data handled, Ms Jagose said.
There were "extraordinary" controls about how data was handled.
"The Inspector-General [of Intelligence and Security, Cheryl Gwyn] can view all of it.
"She can see a complete log of what has happened, and recorded reasons why any of that activity has been taken in relation to that data, or why an analyst is viewing that data.
"We cannot and don't use it for any other purpose. That intelligence - sorry, that information gathered - is used for defending our networks. It is all about cyber security."
Asked if a company's customers would know data may be reviewed by her agency, Ms Jagose said organisations had to advise those who interact with their security systems that communications may be accessed for security purposes.
The number of serious cyber incidents recorded by the GCSB will likely more than double this year, she said.
"Several officials in a key government agency have been directly targeted through email and website exploits in order, we think, to gain access to personal information and maybe compromise that department's network," Ms Jagose said.
"We have identified and resolved a long-term compromise of a major IT firm. We have helped a telecommunications provider respond ... after identifying suspicious overseas activity on their network."
Ms Jagose would not comment on whether foreign governments were behind some of the attacks, saying the GCSB focus was on prevention.
In July, the Obama Administration admitted hackers stole the private information of about 25 million people through two hacks at the United States Government's human resources agency.
James Clapper, US director of national intelligence, said China was the "leading suspect". Last week the US and China announced a cybercrime truce, agreeing neither country would engage in cyber economic espionage.
Ms Jagose said overseas hackers were also using New Zealand computer systems as a "jumping off point".
"They kind of route their malware through New Zealand, maybe thinking New Zealand is something of a soft underbelly of cyber defence, to target overseas networks," she said.
The existence of the Cortex program was first revealed by Prime Minister John Key before last year's election, ahead of Kim Dotcom's "moment of truth" event in Auckland and in response to claims New Zealand had tapped the Southern Cross cable network.
Ms Jagose began her relieving role in March, the same week that documents taken by former US NSA contractor Edward Snowden relating to New Zealand were published by the Herald.
The NSA and GCSB are sister organisations in the Five Eyes intelligence alliance of US, Britain, Canada, Australia and New Zealand.
The revelations included that there was a "full-take collection" of information from New Zealand's Pacific neighbours, sweeping up information from the region and passing it on to the NSA.
Asked after yesterday's speech if she could explain what "full-take" involved, Ms Jagose said it would not be appropriate given the allegations were being investigated by the Inspector-General of Intelligence and Security.
She said no mass surveillance was carried out, and voiced frustration with "misinformation" in some media reporting that had exposed some of New Zealand's vulnerabilities.
"I think it is an issue that I would quite like to talk more with media outlets about - at what point does New Zealand's interests become compromised, and how can we get over that."
• GCSB's cyber security program
• A cyber defence system run by the GCSB, which protects government agencies and some private companies and organisations.
• Cortex is mostly automated, with machines using information and patterns gleaned from previous attacks to scan data and systems for points of weakness and possible intrusions.
• Who gets protection is secret and decided according to criteria set by the Government. More organisations are covered as cyber attacks increase.