The Government did not correct or clarify the description that the Treasury's computer system had been "hacked" for an entire day despite being told by its cybersecurity experts that no hacking had taken place.

On the same day - Wednesday last week, the day before Budget day - the National Party also refused to reveal how it had obtained confidential Budget information, instead accusing the Treasury and Finance Minister Grant Robertson of unfairly smearing National.

Robertson said yesterday that the Government was being tight-lipped because the Treasury had called in the police, but he was also unlikely to want any further distractions on the eve of the Government's much-hyped Wellbeing Budget.

Instead Prime Minister Jacinda Ardern and Robertson spent that Wednesday answering questions about hacking from National MPs in the House, while changing the language to say that the Treasury had been "attacked".

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National is demanding answers after the Herald revealed that Andrew Hampton, head of the Government Communications Security Bureau, made an urgent call to GCSB Minister Andrew Little in an attempt to stop Treasury Secretary Gabriel Makhlouf from publicly saying that his department had been hacked.

National deputy leader Paula Bennett said it was inconceivable that Little didn't pass that information on to Robertson and Ardern straight away, and they should have immediately revealed the advice that there had been no hacking.

"If Mr Robertson received the information from Andrew Little after he released his statement, he should have immediately corrected it," Bennett said.

The GCSB's cybersecurity unit had already told the Treasury it did not think any hacking had occurred, and the phone call was another attempt to prevent Makhlouf from using the term "hacking" in his public statement that was released on the evening of Tuesday, May 28.

Robertson said he was not told about the GCSB's concerns until after the release of statements from Makhlouf and himself, which both described what had happened to the Treasury as systematic hacking.

"I certainly did not know anything other than what the Treasury had advised me when I put the statement out," Robertson said.

Little told NewstalkZB yesterday that he passed on Hampton's concerns to Robertson in a timely way, but would not say whether that was before Robertson released his statement.

"I'm satisfied that I acted appropriately and in a timely way with all the information I had," Little said.

"I know what I know. Grant Robertson knows what he knows, and actually Grant and I know what we each know.

"I'm quite happy and relaxed about anything I had to do in relation to any of this."

Neither Ardern, Robertson, Little or the GCSB would discuss the timing of Hampton's phone call or when they knew about the phone call.

Ardern said yesterday that the State Services Commission investigation into Makhlouf should work out the timeline.

The commission's jurisdiction does not include ministers, and State Services Commissioner Peter Hughes would not say if the investigation into Makhlouf would look into the GCSB phone call.

The National Party has also been criticised for refusing to reveal how it obtained Budget 2019 information on that same Wednesday.

Instead National leader Simon Bridges called a media conference to accuse Makhlouf and Robertson of smearing the National Party, but he batted away repeated questions about how the Budget information had been accessed.

The following morning, on Budget day, Bridges showed media how its staffers had used the Treasury website's search bar to find confidential Budget information.

Hours before that, the Treasury had released a statement outlining police advice that nothing illegal had happened.

Bennett said the National Party would use Question Time in the House next week to seek answers from Government Ministers.