A man from Devon has put details of thousands of paedophiles on a website.
Chris Wittwer has listed 9,500 convicted paedophiles from across the British Isles, saying he wants to help the public and support abuse survivors.
Mr Wittwer said his information was based on media reports, court records and the sex offenders register.
Police and probation staff said they feared the site could endanger the public as it might help drive offenders underground.
Mr Wittwer, 35, from Exeter, who has worked on the site for three years, said he had set it up because he had been abused himself and "child cruelty and child abuse has got to stop in this country".
"I fear at the moment that the government and the police are not doing enough to monitor sex offenders on their release from prison. Too many are going missing," he said.
He added that the website was "not about taking the law into your own hands".
"The website is a tool for parents to take care of their children and look out for their safety. Naming and shaming is a very small part of it," he said.
Mr Wittwer said his website had been checked by police and had also been viewed by staff involved in the Multi Agency Public Protection Arrangements (Mappa) project.
Mappa manages registered sex offenders offenders in the community to prevent reoffending.
Devon and Cornwall Police said the website was not breaking any laws as all the information had previously been published in the public domain by the media following court results.
The force added: "However, it is felt that the collating and publishing of this material raises awareness of where these individuals are living and ultimately may inhibit people's safety rather than protecting it as the offenders may seek to move on without updating authorities, making it impossible to manage them."
The police also said they followed Mappa's nationally recognised protocols in order to manage registered sex offenders in order to prevent re-offending.
The Devon and Cornwall Probation Trust said that it could understand public concern about offenders, but added it also believed the site could mean offenders would be more difficult to keep track of.