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Australia is poised to introduce some of the most severe internet restrictions in the democratic world - and the hackers don't like it.

Yesterday they vented their ire on government websites, shutting them down in co-ordinated attacks and plastering the Prime Minister's home page with pornography.

Kevin Rudd's site became the home, temporarily, of "Operation Titstorm", part of an assault targeting a range of government servers.

The Australian parliamentary website was crippled for almost an hour; among the ministries affected was the Communications Department, which is pressing for a compulsory internet filter for pornography and other "offensive" content.

One cyber security expert, Alastair MacGibbon, described the attacks as "the equivalent of parking a truck across the driveway of a shopping centre so that normal people can't drive in to do their business".

The strikes were launched by hackers aligned with an internet protest group known as Anonymous, which often targets Church of Scientology websites. Although the Australian government knew about the planned assault last Friday, it was powerless to prevent it.

Along with the cyber-offensive there were threatening phone calls, made anonymously to high-ranking civil servants. Senior staff in the Parliamentary Services department also had their emails spammed "in spectacular ways", according to Alan Thompson, the departmental secretary.

The federal government plans to introduce a mandatory filtering system by early 2011 that would block a list of banned websites featuring obscene and criminal-related material.

The system would make Australia one of the world's most rigorous internet regulators.

Critics say the filter will not prevent contentious content being shared, and they fear it could lead to censorship by over-zealous officials.

Australia's sex industry has claimed that some pornographic films are being rejected by censors because they feature women with small breasts who could be confused with under-age girls.

Anonymous said in an email: "No government should have the right to refuse its citizens access to information solely because they perceive it to be 'unwanted'. The Australian government will learn that one does not mess with our porn."

A similar attack last September was also attributed to the group.

Polls have found that the Australian public strongly supports the planned restrictions.

One poll, conducted this week, reported 80 per cent of respondents supported the idea of a filter.

The Communications Department said the hackers had not infiltrated security, but had swamped government servers with a "distributed denial of service attack".

Just after 8am local time, the parliamentary website was hit by 7.5 million requests per second for communication. Further incidents occurred throughout the day.