But on SBS' Insight program last night, Senator Conroy said "it's mandatory refused classification, and then parents - if the trial says that it is possible to go down this path ... have the option to block other material". This about-turn has done little to assuage the concerns of online rights groups, the Federal Opposition and the internet industry, as the RC category includes not just child pornography but anti-abortion sites, fetish sites and sites containing pro-euthanasia material such as The Peaceful Pill Handbook by Dr Philip Nitschke.

Sites added to the blacklist in error were also classified as RC, such as one containing PG-rated photographs by Bill Henson. And the websites of several Australian businesses - such as those of a Queensland dentist - were classified RC and blacklisted after they were hacked by, as Senator Conroy described, "the Russian mob". They were on the blacklist even though they changed hosting providers and cleaned up their sites several years ago. "The guidelines are so broad that RC can't help but hoover up political speech even if only as collateral damage," said Internode network engineer Mark Newton, describing Senator Conroy's comments last night as "the great walkback of 2009".

Senator Conroy conceded many of the decisions regarding what sites appeared on the blacklist were made by "faceless bureaucrats". He said he was working to build in "further safeguards", but would not abolish the policy because some sites were found to be put on the blacklist in error. "I don't think Senator Conroy really even knows what his own policy in relation to filtering is. It seems to change on an almost daily basis; it is vague and contradictory and there is little public confidence in his ability to implement it," said Opposition communications spokesman Nick Minchin.

"RC can apply to a range of different subjects, not just sexually explicit, but also the controversial, which under Labor's proposal would all be filtered." Colin Jacobs, spokesman for the online users' lobby group Electronic Frontiers Australia, said he was pleased the Government was "distancing themselves from the current flawed blacklist, which as we have seen is chock full of legal and harmless sites". But Jacobs was not convinced that a new "RC only" list would be a big improvement.

"Swapping one secret list for another doesn't mean that fewer mistakes will occur or that everything on the new list will be uncontroversial," he said. "Not all RC material is illegal, so we'd probably still see euthanasia sites and the like on the list."

Others sites confirmed by ACMA as being included on the blacklist include a YouTube clip showing an excerpt from a horror movie and an astrology website. ACMA said the horror movie clip was added because it is classified as R18+ but "not subject to a restricted access system that prevents access by children". "At the time of investigation, access to the YouTube content required only a declaration of an age of 18 years or older which was not verified by evidence of proof of age," ACMA spokesman Donald Robertson said.

On the astrology website, ACMA said it was blacklisted because, at the time it was being investigated, it had been defaced with "an image which depicted an adult female posed naked and implicitly defecating on herself". This image has since been removed and ACMA said it was in the process of removing the astrology site from the blacklist.

ACMA conceded innocent sites could be blacklisted if they are defaced with content not usually associated with the site. Robertson acknowledged this material was often only visible for a short period before being removed by the site owner. "To deal with the transient nature of online content, ACMA undertakes regular reviews of the list of URLs notified to filter makers to remove those which no longer lead to prohibited content," he said.