New Zealand's spies are pleading for trust from the public.

Government Communications Security Bureau acting director Una Jagose has made a rare public speech in an effort to clear up misconceptions and myths about the secretive organisation.

The spy agency has faced staunch criticism after revelations, in documents provided by whistleblower Edward Snowden, the GCSB's work included spying on international diplomats in support of Trade Minister Tim Groser's bid to lead the World Trade Organisation, feeding information to Bangaladeshi security forces facing murder and torture allegations, and sending "full take" communications data from the Pacific to the National Security Agency.

Jagose told the Wellington audience it's not possible to do their work and be entirely open with the public about what they do.

"We are, and we must be, utterly open to the oversight bodies. Their reports on us are what should reassure you that what goes on is lawful, proportionate, reasonable, and done with New Zealand's interests at heart," she said.

"We're not simply randomly hoovering up information and rummaging around in it, hoping to find something interesting. That image of mass surveillance is probably one of the biggest misconceptions about the work that we do."

Jagose said hackers are increasingly targeting New Zealanders, with 147 attacks last year and 132 in the first six months of this year. Of those this year, 79 were against government departments and 33 against private sector organisations.

Technology commentator Paul Spain believes one of the reasons is because New Zealand has so many small businesses.

"The challenge with small businesses is that they're not always resourced as well as larger ones and we can be a little bit casual around things such as how we manage our technology security."

Jagose was deputy Solicitor-General before filling Ian Fletcher's position. He stepped down two years before the end of his term.