She said the filter scheme was "fundamentally flawed" because it failed to tackle the problem at the source and would inadvertently block legitimate resources. Furthermore there was no evidence to suggest that children were stumbling across child pornography when browsing the web. Doel-Mackaway believes the millions of dollars earmarked to implement the filters would be far better spent on teaching children how to use the internet safely and on law enforcement.

"Children are exposed to the abusive behaviours of adults often and we need to be preventing the causes of violence against children in the community, rather than blocking it from people's view," she said. "The constant change of cyberspace means that a filter is going to be able to be circumvented and it's going to throw up false positives - many innocent websites, maybe even our own, will be blacklisted because we reference a lot of our work that we do with children in fighting commercial sexual exploitation." Doel-Mackaway noted the claims by the internet industry that the filters would be easily bypassed, would not block content found on peer-to-peer networks and chat rooms and would be in danger of being broadened to include legitimate content such as regular pornography, political views, pro-abortion sites and online gambling.

Laboratory test results released in June by the Australian Communications and Media Authority found available filters frequently let through content that should be blocked, incorrectly block harmless content and slow network speeds by up to 87 per cent. James McDougall, director of the National Children's and Youth Law Centre, expressed similar views to Save the Children.

He said the mandatory filters simply would not work and children should be able to make decisions for themselves. Concerned parents could easily install PC-based filters on their computers if they desired, or ask their internet providers to switch on voluntary filtering. "This is called a child protection measure yet the vast majority of all serious child abuse does not occur on the internet, it occurs in the home," said McDougall. "I take issue with the minister's perspective that children are themselves the danger in a sense that we have to make this decision for them because they are not capable of making it for themselves - I think there's very little evidence to support that and plenty of evidence to show that children are responsible decision makers given the skills and information."

Other childrens' welfare organisations, such as Child Wise and Bravehearts, continue to support the filters, saying the flaws are acceptable as long as they help block some child pornography.

On Thursday, as political activist group GetUp announced its plans for an elaborate anti-filtering campaign, 70 ISP filtering stakeholders converged on the University of NSW to examine the merits of the proposed censorship scheme.

"There seemed to be some consensus that the proposed mandatory filter model would not actually be directed at the real channel of child porn distribution, which is not the blacklist of known web sites, but via various other internet protocols and tools," said David Vale, executive director of UNSW's Cyberspace Law and Policy Centre. "The idea of doing whatever was possible in stopping the problem at the source, including education of parents, kids, teachers and politicians, and serious law enforcement efforts at detection and prosecution of perpetrators and distributors, was seen as probably as, or more, effective than a filter initially aimed at preventing inadvertent browsing of child porn on the web by young people. "Another aspect was the potential for the filter, once in place, to become the subject of a repeated bidding war, depending on which minor politicians had balance of power in parliament, or who had the 'moral panic of the day'."

Senator Conroy's spokesman, Tim Marshall, has consistently failed to respond to requests for comment on the issue.