It is inevitable that people will use the internet to list sexual offenders perceived as a threat, the Sensible Sentencing Trust says.
Radio New Zealand has identified social media sites listing offenders' names, photographs and other details to alert communities of danger.
Sensible Sentencing Trust offending database manager Peter Jenkins said it was only a matter of time before such sites were online.
"Nature abhors a vacuum. We have an information vacuum here and it's going to be filled by something," he said.
"Either the government fills it with accurate, verified information or people will do it themselves and that's what's happening here.
"The only thing that surprises me about this is that it's taken so long to happen."