A Dunedin philosophy student who shared bestiality images online and wrote about his desire to rape babies has been jailed for three years.

Benjamin Todd Whitcombe (22) appeared in the Dunedin District Court yesterday after pleading guilty to four charges of exporting objectionable publications, one each of importing, making, possessing, and possessing objectionable publications for the purpose of supply.

Judge Kevin Phillips said objectionable statements written online about the defendant's predilections were "unbelievably appalling" but he stressed he had to put aside his revulsion and deal with the man in a clinical manner.

Whitcombe admitted in a pre-sentence interview he could not control his urges.

He came to Canadian authorities' attention in December through his use of a messaging app called Kik under the name "Philosophers Stone".

Later analysis of Whitcombe's phone found he uploaded four publications "depicting the sexual exploitation of a child".

An investigation by New Zealand Customs showed the crimes had taken place at a North Dunedin address and at his parents' home.

On April 19, officers executed a search warrant at a North East Valley house where the man was living, during which they seized his electronic devices.

Whitcombe was questioned during the raid and admitted he knew the child abuse material was "bad" and that he had used Kik since he was 14 to communicate with people around the world.

The full extent of the depraved offending though only became apparent when the student's seized devices were forensically examined.

Investigators found another Kik account and traces of child-sex images and videos on a different cell phone.

Further, there was a Tumblr account complete with Whitcombe's photo.

Tumblr is a micro-blogging social-media site on which the defendant went by the name "wanderingphilosopher".

His profile featured the bio: "Into everything and anything twisted . . . Looking forward to conversing with the like minded sick freaks on here. 18+"

Over two years, Whitcombe had messaged 128 other users – but it was 17 exchanges that caught the eye of Customs.

The content of his online statements - in which he expressed a desire to rape babies - was so graphic, court documents had to be redacted, and much of the redacted conversations is still too explicit for publication.

It also emerged Whitcombe had been communicating with a 15-year-old.

Through their discussions, he encouraged the person to engage in sex acts with an animal and at the end of February he received photos showing such activity.

Those images were later distributed by the defendant, using an anonymous file sharing app called Whisper, the court heard.

Crown prosecutor Catherine Ure said Whitcombe's conduct was "sustained and highly premeditated".

Defence counsel Anne Stevens argued her client was suffering from an addiction - "not something one would wish on one's worst enemy".

"He could have possibly graduated with a high academic qualification.

Now he's unlikely to ever do so," she said.

Whitcombe will automatically be placed on the Child Sex Offender Register.