Sex offenders who have had their names suppressed could be avoiding detection because their crimes do not have to be revealed in their criminal records checks.
The Ministry of Justice says about 400,000 applications for criminal records were made last year and it is looking at the way its checks work to make sure they are operating properly.
Sex offenders are often granted name suppression, because if they are a relative or are known to their victim, exposing who they are could easily identify the person they have abused.
The ministry says both it and police can provide information about people's criminal records.
The ministry's criminal record unit was set up to give people access to their own information and they can share this with prospective employers, but it should not be treated as a comprehensive security check.
It says an approved list of employers who work with children or the elderly go through a police vetting procedure designed to flag risks that cannot be disclosed by the ministry.
