More than two dozen New Zealand children have been exploited for online pornography in the last four years, with some of the material traded through criminal networks.

Figures obtained by Radio New Zealand showed since 2008, a special police unit had caught 11 people taking pictures or videos of 26 children.

The figures, released under the Official Information Act, revealed four of the children were exploited by criminals based in Italy, the United States, Finland and Canada where images of the victims were uncovered during international operations, RNZ reported.

The head of the police online child exploitation unit, Detective Senior Sergeant John Michael, said in some cases offenders were working in crime rings.


"(But) while there are rings there, you have individuals that are not part of any group that are able to go to those areas of the internet where they know they'll be able to get images."

He said criminals posed as children on social network websites to find victims who take explicit pictures of themselves.

"It's often associated with teenage risk-taking behaviour.

"But the problem is that once you take an image of yourself and send it to someone else, you lose all control over it and what that does is it opens the door, potentially, for people to say, 'You sent me this image and if you don't send more explicit images, then I'm going to post all of these images to all the people that are in your social networking groups'."

Mr Michael said in many cases, the abuser was known to the child.

A Department of Internal Affairs spokesman said images were getting more violent, showing people being raped or tortured.

The department uses undercover agents to go online to flush out offenders.