University of Sydney associate professor Bjorn Landfeldt said the leaked list "constitutes a condensed encyclopedia of depravity and potentially very dangerous material". He said the leaked list would become "the concerned parent's worst nightmare" as curious children would inevitably seek it out.

But about half of the sites on the list are not related to child porn and include a slew of online poker sites, YouTube links, regular gay and straight porn sites, Wikipedia entries, euthanasia sites, websites of fringe religions such as satanic sites, fetish sites, Christian sites, the website of a tour operator and even a Queensland dentist. "It seems to me as if just about anything can potentially get on the list," Landfelt said. The blacklist is maintained by ACMA and provided to makers of internet filtering software that parents can opt to install on their PCs.

However, if the Government proceeds with its mandatory internet filtering scheme, sites on the blacklist will be blocked for all Australians. The Government has flagged plans to expand the blacklist to 10,000 sites or more. In a special report, written in conjunction with the Internet Industry Association and presented to the Government over a year ago, Landfeldt warned that "list leakage" was one of the main issues associated with maintaining a secret blacklist of prohibited sites.

Julian Assange, founder of Wikileaks, dug up the blacklist after ACMA added several Wikileaks pages to the list following the site's publication of the Danish blacklist. He said secret censorship systems were "invariably corrupted", pointing to the Thailand censorship list, which was originally billed as a mechanism to prevent child pornography but contained more than 1200 sites classified as criticising the royal family. "In January the Thai system was used to censor Australia reportage about the imprisoned Australian writer Harry Nicolaides," he said.

"The Australian democracy must not be permitted to sleep with this loaded gun. This week saw Australia joining China and the United Arab Emirates as the only countries censoring Wikileaks." The leaked list, understood to have been obtained from an internet filtering software maker, contains 2395 sites. ACMA said its blacklist, as at November last year, contained 1370 sites.

Assange said the disparity in the reported figure is most likely due to the fact that the list contains several duplicates and variations of the same URL that stem from a single complaint. Alternatively, some sites may have been added to the list by the filter software maker. ACMA said Australians caught distributing the list or accessing child pornography sites on the list could face criminal charges and up to 10 years in prison. Opposition communications spokesman Nick Minchin said the leaking of the list was irresponsible but highlighted how this type of information could surface despite the efforts of ACMA to protect it, and could be used by those with a perverse interest in its content.

"The regrettable and unfortunate reality is there will always be explicit and illegal material on the web and - regardless of blacklists, filters and the like - those with the means and know-how will find ways of accessing it," he said. "Adult supervision is the most effective way of keeping children safe online and people shouldn't be led into believing by Labor that expanded blacklists or mandatory filters are a substitute for that."

Colin Jacobs, spokesman for the online users' lobby group Electronic Frontiers Australia, said the leak was not surprising and would only get worse once the list was sent to hundreds of Australian ISPs as part of the Government's mandatory internet filtering policy. He said the Government could be considered a "promoter and disseminator of links to some pretty unsavoury material". "The list itself should concern every Australian - although plenty of the material is unsavoury or even illegal, the presence of sites like YouTube, MySpace, gambling or even Christian sites on the list raises a lot of questions," he said.

"There is even a harmless tour operator on there, but there is no mechanism for a site operator to know they got on or request to be removed. The prospect of mandatory nation-wide filtering of this secret list is pretty concerning from a democratic point of view." The Communications Minister, Stephen Conroy, said the leak and publication of the ACMA blacklist would be "grossly irresponsible" and undermine efforts to improve cyber safety.

He said ACMA was investigating the matter and considering a range of possible actions including referral to the Australian Federal Police. Australians involved in making the content available would be at "serious risk of criminal prosecution". "Under existing laws the ACMA blacklist includes URLs relating to child sexual abuse, rape, incest, bestiality, sexual violence and detailed instruction in crime," Senator Conroy said. "No one interested in cyber safety would condone the leaking of this list."