Treasury has confirmed in a statement it was the source of National's Budget 2019 leaks today after its "systems were deliberately and systematically hacked".
The Government has contacted the National Party and asked that they release no further material in light of the data breach.
But National's leader Simon Bridges said via Twitter this evening: "The National Party has acted entirely appropriately. Grant Robertson has falsely smeared us to cover up his and The Treasury’s incompetence. When what has occurred is revealed, he will need to resign."
Earlier today the National Party leaked what it claimed were highly secretive details of the Government's wellbeing Budget, due to be delivered on Thursday.
Mr Bridges said the Government are set to put $1.3 billion into defence, an extra $139 million into forestry, $744 million for District Health Boards, $740 million for international aid.
Confirming the hack this evening Treasury released the following statement:
"Following this morning’s media reports of a potential leak of Budget information, the Treasury has gathered sufficient evidence to indicate that its systems have been deliberately and systematically hacked.
"The Treasury has referred the matter to the Police on the advice of the National Cyber Security Centre.
"The Treasury takes the security of all the information it holds extremely seriously. It has taken immediate steps today to increase the security of all Budget-related information and will be undertaking a full review of information security processes.
"There is no evidence that any personal information held by the Treasury has been subject to this hacking."
Responding to confirmation of the the hack, Finance Minister Grant Robertson said is a statement: "This is extremely serious and is now a matter for the Police".
"We have contacted the National Party tonight to request that they do not release any further material, given that the Treasury said they have sufficient evidence that indicates the material is a result of a systematic hack and is now subject to a Police investigation.
"What New Zealanders care about are the issues that will be dealt with in the Wellbeing Budget on Thursday, and that is what we continue to be focused on."
1 NEWS spoke to Treasury’s Deputy Secretary of Budget and Public Services, Struan Little this morning, before the data hack had been officially confirmed.
"Treasury takes Budget secrecy incredibly seriously so any allegations that there have been a Budget breach of that secrecy will be investigated thoroughly," he said.
"We need to look at if there's any voracity to the claims being made and work that through."
Mr Little said Treasury is "scrupulous" about putting out the right information and ensuring the figures are accurate.