Prime Minister Malcolm Turnbull on Wednesday. Credit:Daniel Munoz Chief statistician David Kalisch and technicians at IBM opted to shut down the website at 7.45pm on Tuesday after a confluence of system failures resulting from cyber interference by as-yet-identified operatives. Among the errors contributing to the fiasco were the failure of a geo-location mechanism to block international traffic and a router overload that triggered a "false alarm" on the system monitors. Mr Turnbull assured Australians that "their data is safe" and said the decision to shut down the website had been taken "out of an abundance of caution" by the ABS. "That is a judgment they made, as the independent statistician - that is their call to make at that time and they made it," he said.

Small Business Minister Michael McCormack and Australian statistician David Kalisch during a press conference on the census. Credit:Andrew Meares Despite the government's assurances, Australian Privacy Commissioner Timothy Pilgrim launched an investigation into whether any personal information had in fact been compromised. Opposition Leader Bill Shorten seized on the debacle, dubbing it "the worst-run census Australia has ever seen" and warning it could damage Australians' confidence in the census and other government institutions. He was joined by Senator Nick Xenophon in calling for an independent inquiry to examine, among other things, the role that inadequate funding of the ABS may have played. Labor stopped short of calling for the resignation of Small Business Minister Michael McCormack, who took on responsibility for the census after the election - the third such third minister in 12 months, after Kelly O'Dwyer and Alex Hawke. Mr McCormack noted the census had been planned for more than five years and "I've been the minister responsible for three weeks". He too applauded the "cautious decision" taken by the ABS, recognising Australians had suffered inconvenience but arguing it was "better to be safe than to be sorry".

Mr McCormack said the apparent cyber interference should be characterised as an attempt to "frustrate" the collection of data, rather than a "hack" or "attack". Earlier on Wednesday, Mr Kalisch had not hesitated in calling it "an attack", telling ABC radio: "It was quite clear it was malicious." The Australian Signals Directorate has been tasked with investigating the source of the interference. Government cyber-security adviser Alastair MacGibbon said the majority of offending traffic came from the US but noted this was not unusual in "denial of service" attacks. "It's equivalent to me parking a truck across your driveway to stop vehicles coming in and out. That is all a 'denial of service' is," he said. "It led to other systems failing, absolutely. But it does not compromise the integrity of data." Three smaller "denial of service" attacks were detected during census day on Tuesday, one as early as 10am. A second attack prompted technicians to block all international traffic going to the website, but that software ultimately failed.After a fourth, "large scale" attack at 7.30pm - peak time for completing the census - the router overloaded and set off a "false alarm" on the system monitor, prompting Mr Kalisch to shut down the website at 7.45pm. The census website remained unavailable as of Thursday evening, but the final deadline for Australians to fill in the census is not until September 23. However, software expert David Glance of the University of Western Australia warned that if the cyber attacks were sustained, the ABS may be forced to abandon the project.

"That's an extreme case but yes that's possible," he told ABC radio. Tuesday night's confusion followed weeks of consternation about privacy, after it was revealed the ABS intended to keep people's names and addresses for four years and link them to other government databases. Shadow assistant treasurer Andrew Leigh stepped up the partisan attack on Wednesday, accusing the government of not adequately preparing for the digital transition of the 2016 census. "When the government made the decision to be online by default, they should have thought these issues through," he said. Government sources pointed out it was Labor that originally decided to move to a digital model in the 2013 budget, bringing forward $68 million in funding to help the ABS prepare.

Loading In a departmental note seen by Fairfax Media, the then Labor government was told the transition would require "significant/redevelopment of infrastructure early in the census cycle" as well as "new, integrated systems and technology". Follow us on Twitter