A shadowy group of cyber-activists blocked key Australian government websites on Wednesday to protest against controversial plans to filter the Internet.
The main government website, www.australia.gov.au , and parliament's www.aph.gov.au were both affected along with the sites for Prime Minister Kevin Rudd and Communications Minister Stephen Conroy.
Web activists had earlier warned the sites would be blocked under what they called "Operation: Titstorm", and threatened to follow up with "porn email, fax spam, black faxes and prank phone calls to government offices".
The campaign, by the anti-Scientology group Anonymous, follows Conroy's announcement in December that Australia would block access to sites featuring material such as rape, drug use, bestiality and child sex abuse.
"The Australian government will learn that one does not mess with our porn," Anonymous said in an email sent to AFP.
"No one messes with our access to perfectly legal (or illegal) content for any reason," it said.
A spokeswoman for Conroy defended the new filter measures and denounced the cyber-attacks.
"Denial-of-service attacks on government websites are totally irresponsible and potentially deny services to the Australian public," the official said.
"The government welcomes public debate on the merits of ISP (Internet service provider) filtering, but denial-of-service attacks are not a legitimate form of political statement."
The attorney-general's department said government experts were working to contain the problem.
"Australian government agencies identified as potential targets by 'Anonymous' were briefed in advance and were provided with suggested mitigation strategies," a spokesman said, without giving further details.
Internet groups and the pornography industry have opposed the filter, while search engine Google says it could block harmless material on areas of legitimate debate such as euthanasia, sexuality and terrorism.
Anonymous, known for its campaign against the Church of Scientology, could not immediately be reached for further comment.
Explore further: The internet is on fire but Snowden's heroes can't save us