New Zealand Cabinet Minister Judith Collins resigned yesterday in what appears to be a direct response to the hacking of a controversial blogger's email.

The resignation is a blow to the ruling National Party, which, while well ahead in the polls, has seen its campaign plan torn apart by a series of unexpected and unwelcome disclosures.

The identity of the hacker, who calls him- or herself "Rawshark", is a mystery.

After leaking the emails and other communications of blogger "Whale Oil", aka Cameron Slater, to campaigning journalist Nicky Hager for a book released two weeks ago, the hacker has been progressively dumping the raw emails online and to media.

Exactly how the emails were hacked is also unclear, but there has been some speculation about a "brute-force" attack — a systematic, computerised search of all possible password combinations.

Ironically, the email that forced Collins to resign does not appear to have been part of that cache. It was received some time last week by the prime minister's office from a source that the office agreed to keep confidential.

Prime Minister John Key released the email when announcing Collins' resignation yesterday, attracting a flurry of complaints to the Privacy Commissioner following the hacking. Whale Oil complained that in releasing it, Key himself breached New Zealand's privacy laws.

The email in question appears to show Collins in communications with Whale Oil, who at the time was running a campaign against the chief executive of the Serious Fraud Office (SFO) and others. The SFO was investigating the affairs of a failed finance company, the executives of which were represented by a PR man that Slater was working with.

At the time, Collins was also the minister in charge of the SFO.

Collins denies any inappropriate behaviour and resigned, she said, to clear her name though a public enquiry.

Whale Oil, meanwhile, has backtracked on comments in that email, saying he embellished a discussion with the minister when passing its contents on to the PR man and others.

According to Hager in his book Dirty Politics, the hacked emails were received earlier this year after a denial-of-service attack on the Whale Oil blog. At the same time as that attack, he surmised, the blogger's email and other information were hacked.

Meanwhile, Rawshark is obviously happy to remain in the shadows. In the wake of the release of Dirty Politics, Whale Oil pointed the finger at Kim Dotcom, with whom he has engaged in robust online sparring.

Dotcom has denied that he is Rawshark.

The chosen moniker of the hacker is apparently a reference to "Rorschach", a character in Alan Moore's Watchmen graphic novels.

"I'm not your run-of-the-mill hacker," Rawshark told Fairfax Media last week. "Which means there aren't many like me out there. Which means that as soon as people understand my motivations, the list of suspects narrows down to one."

Rawshark said he is happy for people to think he is a "15-year-old doing it for the lulz".

"It's safer that way, and it doesn't make a difference towards my goal — which is to take down the network," Rawshark said.

This morning, in the wake of Collins' resignation, Rawshark surfaced again, saying her departure from Cabinet justified his actions.

"This isn't just about party politics, he told Fairfax. "This is a network of politically connected individuals who launder political and media influence for money, power, and personal revenge. I hope it's clear now ... why I thought it was justified to expose them in the way that I did. The sacking of Judith Collins is a good start.''

New Zealanders go to the polls on September 20. With more revelations likely, it is shaping up to be the strangest elections ever.