The Attorney-General's Department has fingered the shift from landline telephones to IP telephony as the trigger for its secretive data retention proposal.
The proposal came to light in June this year, when reports emerged that the Government could require ISPs to retain web traffic data for law enforcement purposes.
Little detail has been made available so far, with the Attorney-General's Department stating that publicising the proposal "may lead to premature unnecessary debate".
Representatives from the department's telecommunications and surveillance law branch told a senate committee hearing Friday that it intended to develop a "national, systemic approach" as technology evolved.
Describing the "good old days" of landline telephones, Assistant Secretary Catherine Smith noted that IP telephony providers would no longer store users' phone records for billing purposes.
"We were told by industry that they may not be retaining this sort of information into the future," she told the senate inquiry into the adequacy of protections for the privacy of Australians online.
"Over time, as telecommunications services such as voice telephony migrate to voice over internet services, less and less information will be stored."
Smith said the proposal sought to confirm that the industry would "continue to retain what they already retain".
However, she would not disclose what data it would require to be retained, nor when the proposal was first introduced.
She said the department had consulted widely with ISPs, carriers, State and Commonwealth agencies, the Department of Prime Minister and Cabinet, and industry associations such as the Communications Alliance.
But committee member Senator Scott Ludlam argued that "we seem to have missed out all of civil society, the public and parliament, and the industry associations have been bound by non-disclosure agreements".
Australian Federal Police Assistant Commissioner Neil Gaughan told the committee about a 2008 child abuse investigation, Operation Centurion, that required police to access IP addresses and metadata to identify offenders.
"All I'm asking for here is for the status quo to remain," Gaughan said.
"I think the balance [between privacy and law enforcement capability] is right at the moment; we get access to the metadata which is what we ask to be retained."
The data retention proposal has been criticised by privacy advocates and organisations such as Electronics Frontiers Australia.
EFA chair Colin Jacobs told the committee that retained metadata could be used to build invasive profiles of citizens' habits.
"I haven't heard a compelling case that the system we have right now is broken," he said.
"Until I hear a compelling case that there just isn't enough data... we certainly cannot support that data retention proposal."