Federal senators are prevented from researching online because of repressive Internet content filters which have been installed within the offices of parliament.

The filters have returned a spate of false positive results, preventing senators from researching everything from gun control to breast-feeding. The technology reportedly blocked a news report on carbon emissions, which had no trace of "illicit" material.

Content filtering was installed on senators computers in April, after Senate President Alan Ferguson gave the green light to deploy the technology across wider parliament. Initially only public computers had Internet restrictions.

Democrat leader Lyn Allison said the content filters are ineffective and unnecessary.

"My objection is that the government has a filter to stop us accessing what we need to," Allison said.

"Someone's definition of inappropriate material included things that I research as part of my portfolio, like licit drugs, sexual and reproductive health and illegal weapons.

"The president of the Senate said that [the content filter] would work similar to e-mail filters, but my e-mail if full of ads for Viagra and half of my mail ends up in quarantine so I have to trawl through that anyway."

Privacy advocates said the failure of content filtering in parliament indicates the problems which will occur if the government goes ahead with its plan for national Internet censorship.

A spokesperson for the Democrats said the content filters have blocked legitimate Web sites and allowed pornographic material to be downloaded. He said he has been "testing the perimeters" of the technology by visiting illicit and clean sites, and pages with "borderline" material.

The April changes affect members in the department of Parliamentary Services, Senate, and the House of Representatives.