Internet service providers will soon be able to block customers from accessing child pornography websites using "filtering" software bought by Internal Affairs.
The department has spent $150,000 on the software which blocks more than 7000 objectionable websites and will make it available to ISPs within the next few months.
Customers of ISPs using the filter who try to access any of the websites will see a webpage telling them the site has been blocked because it is illegal.
Internal Affairs has trialled the software with ISPs Vodafone, TelstraClear, Maxnet and Watchdog. Telecom spokeswoman Emma-Kate Greer said it was having discussions with the department and was reviewing the filtering scheme before deciding whether to join.
Netsafe executive director Martin Cocker welcomed the move but said some filters had a negative effect on internet performance and could block the wrong sites.
Filters could also give people a false sense of security, he said.
TelstraClear spokesman Matthew Boland said it would continue to use the software and customers had been positive about the trial.
The filter had not affected internet performance and he was not aware of any sites that had been wrongly blocked.
Vodafone spokesman Paul Brislen said it would also continue to use the software.
Internal Affairs deputy secretary Keith Manch said that during the two-year trial, the filter had blocked "hundreds" of attempts to access objectionable websites.
The software was not a silver bullet that would prevent everyone from accessing any sites that might contain images of child sexual abuse but would help in the fight against such offending.
Bloggers fear it could be used to censor legitimate sites and have called for the list of blocked websites to be made public.
Mr Manch said only websites that hosted child sex abuse images would be blocked. The scheme would remain voluntary and ISPs could opt out at any time.
Anyone who felt their access to a website had been wrongly blocked could ask anonymously for the filter to be checked. The filter would not be used in law enforcement.
The department would establish an "independent reference group" to oversee the scheme, he said.
It would not make public a list of blacklisted websites, as this could lead to further offending.
Australia is trialling a mandatory filtering scheme that blocks Australians from blacklisted sites. Some ISPs have refused to take part in trials of the scheme, which human rights and privacy groups say threatens freedom of speech and amounts to state censorship.
- The Dominion Post