Overseas blackmailers regularly hitting Kiwi users of Ashley Madison website.

Ashley Madison blackmail has hit New Zealand.

Extortionists are using data hacked from the cheating website to track down Kiwis and demand thousands of dollars not to inform cheaters' partners and families.

The nation's internet safety organisation is now receiving several reports a day, compared with none two weeks ago.

"It's taken this long for the cyber criminals to go through it [the dump of hacked data] and match up the Ashley Madison profiles with other information they have on people," said NetSafe's executive director Martin Cocker.

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"So now people are getting their specific blackmail."

But victims appear coy about calling the police. Herald on Sunday inquiries revealed that in the past month just three blackmail attempts linked to the site had been laid with police.

Cocker said the cyber criminals were demanding amounts ranging from $600 to $5600 after tracking down New Zealanders who have accounts with the website, contacting them by phone or email.

The blackmailers usually wanted payment in bitcoin, an internet-based currency often used by cyber criminals because it can't be traced.

It appeared they were operating from offshore.

Netsafe did not pass the complaints to police because the cyber criminals would be almost impossible to catch - the resources needed would not justify the outcome.

"I know for the people being blackmailed that's a terrible thing, but the reality is that the police have got to chase crimes that could possibly be resolved," Cocker said.

Some of the callers to NetSafe were distressed, particularly those who had secrets they didn't want to become public.

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"In the case of Ashley Madison blackmail their options are pretty limited," Cocker said.

"We certainly would never recommend paying because the data is public. It's not as though there is a single copy of something you could pay to have destroyed.

"You'd simply be buying time and you mightn't be buying very much time."

Earlier this year hackers infiltrated the Ashley Madison site, which encourages married people to have an affair, exposing potentially millions of would-be cheaters and as many as 22,000 New Zealanders, including those linked to schools and Government departments.

Cocker said it was hard to judge how many New Zealanders were being blackmailed based on the numbers who decided to report to Netsafe, he said.

"It certainly won't be all of them."

Professor Ursula Cheer, dean-elect of law at Canterbury University, said the Ashley Madison blackmail was a police matter because it was a crime affecting New Zealand citizens.

Police could use computer forensics experts, Interpol and agreements with various countries, much as they did to track down paedophiles, she said.

But the resources required would mean it was unlikely they would be found.

The Privacy Commissioner advises victims who receive Ashley Madison blackmails to refer the matter to the police.

A spokesman said it was possible someone could make a complaint about the way personal information was used under the recent Harmful Digital Communications Act, which placed greater restrictions on using publicly available information unfairly or unreasonably.