National MP Mark Mitchell has categorically stated that National's cache of Budget documents came from a leak, not a hack of the Treasury website.

The Rodney MP said National had instead been leaked "authentic, legitimate and 100 per cent legal information around the upcoming Budget".

"Let me be very clear that the information we have was gained legally and it was not from a hack...it hasn't been stolen, that will be borne out," he told Newstalk ZB's Mike Hosking this morning.

His categorical denial comes after Treasury Secretary Gabriel Makhlouf said Treasury's website had been subject to more than 2000 hacking attempts over a 48-hour period, starting around midnight Sunday.

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Those attempts appeared to be aimed at sensitive Budget-related material.

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But Makhlouf would not or could not confirm whether National's Budget information had come from the Treasury website.

And Mitchell said it appeared the hack and the leak were two unrelated events. He told Hosking he was disturbed that Treasury had not picked up the hack when it happened.

He said the Government was using the opportunity to "smear" the Opposition.

On the same programme Labour MP Stuart Nash said the use of hacked material would be "dirty politics" but that legitimate leaks were fair game.

He said the first thing he would always do when given leaked information was ask where it had come from.

"If someone said to me, 'Well it was leaked by a disgruntled staffer,' then you go 'OK, game's on'.

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"If it was said it was gained by illegal method, then you go 'Well I'm not going near this'. I think the first thing that Simon Bridges or his team or National would have asked is, 'Where did this information come from?' "