Police say the defendant, aged in his 50s, used an online file-sharing platform to download the material between January 29 and May 7 last year.
When his home was searched on May 16, police seized a laptop from his bedroom on which was found about 80,000 photos and 1300 videos of child porn.
About 500 images and 1200 movies were classified under United Kingdom sentencing guidelines as being of the worst type of material, including penetrative sexual activity, sadism and bestiality.
The defendant, who was granted permanent name suppression at his sentencing in the Queenstown District Court yesterday, denied the allegations for two months before admitting three charges of possessing objectionable publications (child sexual exploitation).
He told police he knew it was wrong, but "became obsessed and couldn’t control my actions".
However, earlier this year he changed his story.
He claimed he had been working to "infiltrate and sabotage" the distribution of child porn on the dark web.
Summarising those claims, Judge Russell Walker said the man had "stumbled across" child pornography and been "appalled" by what he saw.
He had undertaken research in order to prepare a comprehensive report for authorities on how to combat it.
The work was "righteous and necessary", and none of the material he had downloaded was for his personal sexual gratification.
That explanation, which the defendant had not given to police after his arrest, was "fanciful", Judge Walker said.
A forensic analyst could find no evidence of the claims, such as documents detailing sources of child porn, an internet search history about agencies combating child porn, or correspondence with such organisations.
A psychologist’s report said the defendant had reached "breaking point" as a result of loneliness, work and family stress, and turned to alcohol and child porn to escape reality.
Judge Walker told the defendant the material found in his possession was "vile", and men like him caused immense suffering to the victims.
"Your actions have helped to fuel the abhorrent international demand for such material."
From a starting point of three years’ prison, he applied discounts for the defendant’s lack of previous convictions, guilty plea and personal circumstances to come to a term of 23 months’ prison.
He converted that to a final sentence of 12 months’ home detention at a Queenstown address.
The psychology report had concluded the defendant was unlikely to pose a risk to the sexual safety of children, so he did not consider it necessary to put him on the child sex offender register.
He had granted the defendant’s application for permanent name suppression only for the benefit of his adult child, who "should not have their reputation tarnished in any way by your wrongdoing".
