National leader Simon Bridges is adamant that his party has acted legally while revealing sensitive Budget documents.

Bridges will not say how National got the information - but insisted today that it was not hacked from the Treasury's website.

Asked if he might have received stolen information, Bridges said National had acted legally and appropriately.

The Treasury revealed today that 2000 unauthorised attempts had been made to hack its website in the past two days.

But Bridges said that National had acted entirely appropriately and the Government was trying to gag the Opposition and conducting a "witch hunt".

He said that was undemocratic of the Government, and the Opposition had not done anything illegal.

The National Party had never done anything like hacking, Bridges said.

Bridges would not say how National obtained the Budget information that it released yesterday.

He said Finance Minister Grant Robertson was smearing National and went so far as to say Robertson was "lying".

"Grant Robertson has made scurrilous false allegations," Bridges said.

He believed Robertson was "bumbling and incompetent".

Robertson needed to say what he meant by linking hacking to the National Party.

"That is a smear on the National Party," he said.

"We have acted entirely appropriately. We have done nothing illegal.

"Grant Robertson has been freaking out over this. They are in a frenzy over this... They then decide to lash out. They are going for it... looking for scapegoats, for people to blame.

"The National Party has acted entirely appropriately... and I think Grant Robertson knows that," Bridges said.

"Right at the moment, he's [Robertson] defaming the National Party ... You are lying.

"He is saying right now the National Party has obtained the information as a result of a hack. He has implied [that] quite clearly. He has no basis to say that. It is for him to front up on that."

Bridges added that he did not intend to release any further Budget information today, which is what Robertson asked of him last night.