An anonymous New Zealander fed up with hoons causing havoc on the country's roads is getting even.

Armed with cans of expanding foam, he has been targeting cars with big exhaust pipes.

He calls himself "The Phantom Expander".

New Zealand's hoons are known as boy racers and they have been big news this week, after 300 of them ambushed a police officer in Christchurch and hurled beer bottles at him.

The government is now considering introducing a law, allowing police to confiscate and crush the cars of bad behaving petrol heads.

But in Blenheim, a little city right at the top of the south island, one local has come up with his own form of punishment, and it comes in a can.

Lance Dodd is editor of Blenheim's local newspaper, the Marlborough Express.

"Last week we received an anonymous letter from someone who signed it 'The Phantom Expander' and he was saying he's taken it upon himself to respond to the socially maladjusted Blenheim pinheads that have chosen to have wide mouth boy racer exhaust installed on their car," Mr Dodd said.

"And he went on to say he was now taking action and squirting builders foam, the expanding foam, that sets hard, into the exhausts of these cars, and that he would carry on doing it."

But the paper does not print anonymous letters, so they told their photographers to hit the road and find some victims.

Blenheim has only got 10,000 residents, and it was not long before one snapper hit the jackpot.

"Our photographer just happened to notice a car as he was walking down the street. It had white foam in the exhaust," Mr Dodd said.

"So he took a photo and we looked up the registration and found out who it was and called here. She was most alarmed to discover that her car had been foamed.

"If you don't pick it up before it gets hard - it actually gets rock hard - and according to the muffler shop, it can cause your exhaust to blow, it can cause your cylinder gaskets to blow."

In his letters to the paper, "The Phantom Expander" says he is carrying out a public service.

Police say he has managed to fill the exhausts of a dozen cars.

One victim was a police officer.

"We have no idea whatsoever [who it might be]," said the officer.

"We've asked anyone if they have any ideas whatsoever to get back to us, so we'll probably get a few crank calls, but hopefully somewhere, someone will know who he is and get a hold of us."

Mr Dodd says what is interesting is that compared to other cities in New Zealand, Blenheim does not really have a boy racer problem.

"It's all in the news, obviously because of what's been going down in Christchurch, they've had huge issues there. No, we don't have that problem, we've got a couple of hoons that drive around every now and then with loud exhaust and things, but you know, no more than any other average town," he said.

"You do kind of smile wryly when you hear and think 'yeah, good on him', but at the end of the day he is breaking the law, some of the people he has targeted are not boy racers or even hoons, just regular guys that happen to have an exhaust that he feels is too big."