Amy Adams has lashed out at the Finance Minister over Treasury secretary Gabriel Makhlouf's absence from a briefing on Budget 2019.
Adams, the National Party's finance spokesperson, said it was "unacceptable" that Makhlouf didn't show up to the Finance and Expenditure Select Committee on Wednesday.
"It's utterly unacceptable that the secretary, who's still on the payroll, is not here filling his role in the Budget that he was in charge of preparing," Adams said.
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Finance Minister Grant Robertson told Adams: "That's entirely a matter for the Treasury and for them to decide who is here.
"I have complete confidence in Mr Little to be able to assist me," he added, pointing to Struan Little, deputy secretary of Budget and Public Services, who sat beside him.
"He is the executive leadership team member who has the oversight of this process, and so I believe we've got the people here who can answer."
Adams responded: "It's not a question of confidence in Mr Little - I regard him very highly as well - but Mr Makhlouf is on the payroll, he prepared this Budget, and he should be sitting beside you."
Makhlouf is currently being investigated over his allegations of hacking in relation to details of Budget 2019 being released by the National Party ahead of its official release date.
The outgoing Treasury secretary - who's set to become Ireland's next Central Bank governor - publicly claimed on May 28 there were "multiple and persistent" attempts to access classified Treasury information.
It prompted the Finance Minister to issue a statement on May 28 following the Treasury's lead by describing a "hack" and publicly naming the National Party.
But the day Budget 2019 was released, National leader Simon Bridges revealed a search tool on the Treasury website had been used to uncover the classified material - no hacking.
A few hours prior, Treasury admitted it hadn't been hacked, prompting accusations the Government misled New Zealanders by allowing them to think Treasury had been hacked, despite the GCSB advising otherwise.
Murray Jack is now leading a State Services Commission investigation into whether Treasury misled the Finance Minister before he issued his public statement echoing the Treasury's stance that it had been hacked.
When asked at select committee why Budget information was freely available through the search function on the Treasury website, Robertson said the investigation would provide those details when it's concluded.
"That's the subject of an inquiry by the State Services Commission, in addition to the investigation that's underway into the advice that I was given about that matter, and so I will await that inquiry with interest."
Adams said Treasury spent $11 million last year renovating their offices, and asked how much money had been spent on upgrading cyber-security to ensure information management slip-ups don't occur.
Robertson said he didn't have the details of spending, but insisted there had been a "certain amount of stress testing, penetration testing on the website".
Adams replied: "Clearly not enough."
Little said Treasury spends about $5 million a year on "normal investments", and part of that is looking at its IT systems and security.
He said while regular system testing occurs, "there's clearly vulnerability in our system, and we're looking forward to working with Mr Murray Jack in terms of how we resolve those and the lessons learnt".