The NSW Director of Public Prosecutions has slammed the Federal Government's internet censorship policy, saying it will have very limited, if any, success in achieving its aims.

Nicholas Cowdery, QC, made the comments in response to a question from a journalist at a conference on e-crime in Sydney yesterday.

"Where will the line be drawn?" ... the Director of Public Prosecutions, Nicholas Cowdery, QC. Credit:Kate Geraghty

"Crime prevention methods need to be practical ... I'm not an expert in the field, but talk of filters, blocking mechanisms and all of that sort of thing, I think, ultimately, in a society like ours, are going to have very limited, if any, success in achieving the aims that their proponents set out for them," he said.

The Government plans to implement mandatory filters in ISPs that would block, for all Australians, sites that have been "refused classification" by Australian regulators.