Det Ch Supt George Clarke, head of the PSNI's Public Protection Branch, said it was a "despicable crime".
"What we are talking about here is people viewing imagery of children being raped, being brutalised, and being physically abused," he added.
"This criminal activity touches every part of Northern Ireland, and every part of society here, and we have some very dangerous offenders here."
He also had this warning for those involved in this kind of crime.
"Offenders need to know the internet is not an anonymous place, it is not a safe place, it is a place where law enforcement is looking for them, where law enforcement is going to find them, and they will face the full rigour of the law when caught," he said.