Mr Porter said given the significance of a free press as"a principle of democracy",it was appropriate to take the step.
"This will allow the most detailed and cautious consideration of how an allegation of a serious offence should be balanced with our commitment to freedom of the press,"Mr Porter said.
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"I have previously said that I would be seriously disinclined to approve prosecutions of journalists except in the most exceptional circumstances and would pay particular attention to whether a journalist was simply operating according to the generally accepted principles of public interest journalism."
He said where the CDPP independently considered that there was a public interest in a prosecution for one of the relevant offences involving a journalist,the consent of the Attorney-General of the day would also be required"as a separate and additional safeguard".
In the High Court submission,News Corp lawyers accepted the need for governments to keep some information secret but questioned the legitimacy of the laws being applied.
The relevant law is a section of the Crimes Act that prohibits the unauthorised communication or release of classified information.
"Its purpose is the protection of government secrecy as an end in itself,whenever that is thought desirable by the Executive – and that purpose is illegitimate,"the lawyers argued in their submission.
They argued the application of criminal law to prevent the release of embarrassing information was incompatible with the implied freedom of political communication flowing from the constitution.
"The entire basis of the implied freedom is that that system depends upon free communication about government and political matters."
A spokesman for the ABC said on Monday the directive was"a welcome step".
"It is one plank in a raft of legislative reform that the ABC identified in its submissions to the two concurrent media freedom parliamentary inquiries,"the spokesman said.
"The ABC looks forward to seeing the recommendations from those inquiries as well as an expeditious conclusion to the current AFP investigation into ABC journalists."