UPDATED 6.45pm: A 60-year-old businessman has been arrested regarding a threat to contaminate infant formula with 1080 poison.

It's believed the man was acting alone. 

LISTEN: Police Commissioner Mike Bush briefs the media on the arrest 

Police have made the announcement at a media briefing in Auckland today.

He has appeared in court on two counts of blackmail following the threats made in November last year.

The man was granted interim name suppression and remanded in custody until later this month,

Police Commissioner Mike Bush says the arrest follows a long and complex investigation "and it reflects how seriously we view crimes of this nature."

In November last year, Fonterra and Federated Farmers received letters threatening to contaminate infant formula with 1080 poison.

It's involved more than two and a half thousand people and cost more than $3 million.

Commissioner Mike Bush says today's arrest comes after five search warrants were executed today in Auckland and Rangitikei.

"The arrest follows a long complex and comprehensive investigation. It was oe of the biggest investigations police has undertaken in recent years," Bush reported. 

"Those charges of blackmail are punishable by up to 14 years imprisonment."

Ministry for Primary Industries chief executive, Martyn Dunne, says the arrest marks the end of a lengthy police operation and the threat which was made against the most vulnerable in New Zealand.

"Today Mums and Dads should be confident the infant formula and the food that's involved in the industry is as safe today as it was then."

Fonterra has thanked the police and the Ministry for Primary Industries for their efforts in their investigations.

Chief executive Theo Spierings said he's pleased to hear an arrest has been made in the case.

He said their efforts on behalf of the New Zealand dairy industry, retailers and the general public have been exhaustive.

Police Minister Michael Woodhouse said the arrest is a milestone in what's been a long and complex investigation and he's thanking police for their efforts.

Meanwhile Green Party Co-Leader James Shaw is also welcoming news an arrest's been made. He's commended the great police work, as he hadn't held out much hope that they'd find the suspect.