SYDNEY, 22 MARCH 2011 - Facebook and three of Australia's largest web companies have criticised Labor's planned mandatory internet filter, saying it is not the answer to protecting Australians from the web's worst excesses.

The comments - by security experts who are employed by Yahoo, ninemsn, Microsoft and the social networking pioneer Facebook - were delivered during a hearing of the joint select committee on cyber safety, formed to inquire into how best to protect Australian children online.

''I would hate for the public to get the wrong impression that there is a quick technological solution for inappropriate content, because there isn't,'' Facebook's chief privacy adviser, Mozelle Thompson, told the committee.

The views are in stark contrast with those of the Communications Minister, Stephen Conroy, who has championed a mandatory filter since it was announced in 2007.

Online identity fraud and distribution of child abuse images has grown sharply in recent years. Mr Thompson said Facebook banned as many as 20,000 user accounts a day. Some are blocked due to inappropriate content.

Labor's proposed filter will prevent blacklisted websites from being allowed past Australian internet service providers. That would mean Australians would be unable to access those sites.

Opponents of the filter, which include Google and the US government, argue it would not only be unable to stop inappropriate material from slipping through, it sets a dangerous precedent for web censorship.

The companies' responses came after a question asked by the Liberal backbencher and filter opponent Alex Hawke.

''Our view is that that decision was made very quickly and that we believe that it would be good to see the possibility of a voluntary program explored,'' ninemsn's Jennifer Duxbury said.

She said voluntary filters had worked well overseas.

Yesterday a spokeswoman for Senator Conroy issued a media release responding to the companies' comments. ''There is no silver bullet when it comes to cyber safety,'' the statement said.