An Attorney-General's Department spokesperson confirmed to ninemsn the Prime Minister's website was taken down at 7.25pm last night, but said the site was operational again "within minutes".

"Visitors to the site received a service unavailable error," the spokesperson said in a statement.

"There was no unauthorised access to site infrastructure."

The Australian Communications and Media Authority's website was also affected.

A message posted on the Inquisitor website by Anonymous stated that the action was in response to a federal government proposal to introduce mandatory internet filtering.

The posting, titled "Anonymous vs the Australian Government", also gives a blow-by-blow account of progress of the hack.

"In two minutes from when I type this, Anonymous is declaring war on the Australian Government over its decision to implement Draconian internet censorship," the posting said.

"Tick tick tick.

"Update: 7pm: and so it begins.

"7:05pm (AEST), Ministers page is slow to load, but still up."

"7:11pm we've confirmed on site (via a source) that the sites due to be attacked have been taken down from the coordination page, possibly before the raid."

"7:18pm pm.gov.au DOWN!

"7:21pm Kevin Rudd's page is down completely. Strike one to Anonymous."

This follows a video posted to YouTube on August 8, which threatened to unleash an online campaign against Kevin Rudd over the internet filter.

In the video, Anonymous demanded the censorship plan be abolished and the resignation of Stephen Conroy, the Minister for Broadband, Communications and the Digital Economy.

Anonymous is notorious for hacking high-profile targets and was most recently in the news after it targeted starlet Miley Cyrus's website.

An Anonymous member was behind the hacking of US vice-presidential candidate Sarah Palin's email account and the group famously declared war on Scientology.

The website 4chan.org, a favourite haunt of Anonymous members, has been identified as a likely target for the internet black list.

A spokesman for Communications Minister Stephen Conroy said he had received reports of the hack but could not confirm whether the attack had been successful.

However, he said the people responsible were misguided, adding that the proposed filter would only be used to block illegal content.

"The campaign that they're mounting is erroneous and misinformed," he said.

"What the government is proposing is to filter refused classification content which includes imagery of child sexual abuse, rape and bestiality."

The government has been conducting an internet filter trial which is expected to be completed soon.

A report will then be presented to Senator Conroy from which an internet filter policy will be developed.

Lobby group GetUp!, a vocal opponent of the proposed filter, said it didn't condone the hackers' actions but it showed flaws in the government's plans.

"We don't support those kinds of illegal actions, but what it does show is that the government, in fact, will have a very difficult time keeping up with the direction the technology is moving in," GetUp! National Director Simon Sheikh told ninemsn.

"A mandatory internet filter is designed to keep up with the pace of technology, and that's simply not possible as these events have shown."

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