The attacks come as the government prepares to introduce its controversial mandatory internet filtering legislation and just after the Australian sex industry claimed porn films were being banned from sale in Australia because they featured small-breasted women and female ejaculation.

The Classification Board confirmed that pornography could be banned if participants simply "appeared" to be under age, while female ejaculation was considered a form of urination, which is banned under content classification guidelines.

In an email sent to media yesterday afternoon foreshadowing the attacks, Anonymous referred to the internet filtering legislation and the perceived pornography censorship.

"No government should have the right to refuse its citizens access to information solely because they perceive it to be 'unwanted'," the email read.

"The Australian government will learn that one does not mess with our porn. No one messes with our access to perfectly legal (or illegal) content for any reason."

In the flyer recruiting people for the attacks, Anonymous said the attacks on the websites would be followed by "a shitstorm of porn email, fax spam, black faxes and prank phone calls to government offices (emails/faxes should focus on small-breasted porn, cartoon porn and female ejaculation, the 3 types banned so far)".

A spokesman for the Attorney-General's Department said government agencies identified as potential targets by Anonymous were briefed in advance and provided with suggested "mitigation strategies".

"Australian Parliament House website (www.aph.gov.au) was unavailable this morning for approximately 50 minutes due to a distributed denial of service attack by individuals belonging to the 'Anonymous' group. It is now back online," the spokesman said.

"The Department of Broadband, Communications and the Digital Economy’s website has also been experiencing a degraded service.

"The Department of Defence Cyber Security Operations Centre continues to monitor the situation."

Speaking to the ABC's Hungry Beast this week for a segment on the government's internet filtering policy, which airs tonight, Senator Conroy laughed off the Anonymous threats. He said the hackers themselves described last year's attack on government websites as "shockingly disappointing".

Anti-censors hip groups in Australia, including stopinternetcensorship.org and the System Administrators Guild of Australia, have condemned the attacks, saying it hurts their cause.

"It would be much more helpful for these people to put their efforts behind legitimate action to stop this ineffective and inefficient attempt at censorship by the Australian government," Stop Internet Censorship co-founder Nicholas Perkins said.