Parents, dairy industry heavyweights, authorities and 1080 protesters have criticised the person or group responsible for the threat, made in November in letters to Fonterra and Federated Farmers but revealed yesterday afternoon.
The anonymous letters contained milk powder laced with 1080 and stated formula would be contaminated with 1080 if New Zealand didn't stop using it by the end of this month.
Prime Minister John Key called it a "form of ecoterrorism" and said while police felt the risk of the threat being carried out was low, the matter was being taken seriously.
"I want to reassure parents that every step possible has been taken to respond to the threat, to ensure the ongoing safety of our food products."
Foodstuffs, which owns Pak'nSave and New World supermarkets, said it was doing everything to ensure infant formula in its stores was safe. The company said it had put additional security and controls in place.
Countdown acting managing director Steve Donohue said extra security measures at the group's supermarkets included the constant monitoring of infant formula product.
"Some of these security measures will mean it takes a little bit more time for customers to purchase infant formula, but together these steps will ensure constant monitoring of the product, either in person or by CCTV," he said.
This morning, a spokeswoman from Countdown said all infant formula had now been moved, either behind service desks or Lotto counters, depending on store layout in all Countdown, FreshChoice and SuperValue stores.
This made it easier for all product to be monitored either in person or through CCTV, and was just one part of a number of measures Countdown was taking in all its Distribution Centres and stores.
She said it was too early to understand how customers were feeling "We're just focused on doing what we can to keep infant formula safe and importantly, reassure our customers that there is product for them to buy for their babies and toddlers."
Industry chiefs reacted angrily, with New Zealand Infant Formula Exporters Association chief administration officer Chris Claridge saying it was "the work of a nutter", Paul McGilvary of the Tatua dairy co-operative labelling it as "blackmail against New Zealand" and the New Zealand Food & Grocery Council calling the person responsible a "coward".
Speaking to TV3's Firstline this morning, Ministry for Primary Industries deputy director general Scott Gallagher continued to reassure parents that infant and milk formula products were safe.
"Mums and dads can be assured that the product on the shelves today is as safe as it was prior to the threat," he said.
Mr Gallagher said from the beginning, MPI had been focused on the protection and well-being of all consumers.
He said they have been working with manufacturers and retailers to put in place a wide range of extra security and mitigation measures.
"We have instituted a new testing regime to go on top of and complement our already strong and comprehensive testing regimes."
The ability for anyone to be able to contaminate any products was "low", Mr Gallagher told the programme.
"We have been focused upon working with manufacturers and retailers to tighten up the security and vigilance across the whole supply chain, therefore eliminating any of the possibilities of someone intervening at any stage to contaminate."
Prime Minister John Key told TV3's Firstline that there were several reasons as to why any threat was not revealed to the public earlier.
"The police needed to undertake an investigation and have been doing that for the last few months.
"Secondly we needed time actually to develop a test for 1080. Because it's not in milk powder, it's one of those things where they have never tested for before, so we actually needed to develop a test.
"Third thing was we needed to lock down... the whole issue around supply chain of 1080, they actually need to run tests on the sample that was sent in by this 'nut job'.
Mr Key said he believed it was "the best thing to do" to wait and reach a point where consumers could be assured that what was in the cans was safe and had been tested.
He told the programme he was never tempted to treat the letter as a hoax, and it was not an option for the government to "close its eyes and pretend it was not aware".
"Ultimately if we did that and then something occurred of course we would have to take responsibility for our actions.
"The moment the head of Fonterra got that letter... I was told very shortly after that.
"In reality while the probability of this being a hoax is extremely high, and the probability of it then being carried out is minutely low - it's just not an option for the government to close its eyes and pretend it's not aware of it."
Long-time 1080 opponent Tony Orman described the method of protest as "totally irresponsible".
"I can understand people being absolutely frustrated with the Government's pig-headedness around 1080 and the continued use of it ... and I'm not surprised at their frustration. But I don't condone their form of protest."
Waikato Regional Councillor Clyde Graf, who has spent many years highlighting the risks of 1080, said the threat was a "random act" that didn't reflect the actions of those opposed to the use of 1080.
Dorothy Waide, who works with parents of young babies, said 1080 should not be used while it was not known if the threat was genuine.
Many parents the Herald spoke to were more outraged that someone would threaten children than fearful the product would be contaminated.
An Auckland father, who gave his name as Johan, said it was beyond belief that any protester would threaten products for children to further their agenda. "It's quite sick."
Parents took to social media to condemn the threat.
"Pretty scary as a mum to see this," Amanda Linn posted on the Mums on top Facebook page. "Disgusts me, even if it is a hoax."
Nichola Ahlers said: "It would be extremely difficult for someone to contaminate it ... Just another crazy nut job."
Fonterra chief executive Theo Spierings labelled the threat a "despicable act".
His main priority was to protect consumers and "robust" testing had not shown any sign of the chemical.
"Our product is safe - as an industry we will be ... working together."
Federated Farmers president Dr William Rolleston said the Ministry for Primary Industries had implemented a comprehensive 1080 testing regime in dairy processing plants "which should allay consumer concerns".
The use of 1080 was both a vital and safe means of controlling the spread of bovine tuberculosis (Tb) between New Zealand dairy herds.
"I am confident from what I've seen that our regulatory authorities and processors have created formidable barriers to any such threat being carried out," he said.
Nathan Guy, Minister for Primary Industries, said the threat was "absolutely appalling".
Forty-thousand tests were carried out in recent weeks and 20 manufacturers contacted but he said no traces of 1080 were found in any of the tested products.
Mike Clement, police deputy commissioner of national operations, said up to 36 staff had been recruited to investigate the 1080 threat since November. While it was possible the threat was a hoax, it was important to treat it seriously.
It was the second time a letter threatening 1080 poisoning had been sent. In 2008 police investigated 16 letters to local body, central government agency and private business addresses.
"The letter writer may not have really considered the implications of their actions when this communication was drafted," Mr Clement said of the current threat.
He also appealed to the public for help: "You might be aware of someone who has strong views [about] 1080 and has made threats. Please make contact with us."