IBM has confirmed it is sitting out the project to develop, host and support the online platform for the next census.

The bureau, which is looking to avoid a repeat of the two-day shutdown that shredded its reputation for IT in 2016, expects three quarters of the nation's households to complete the 2021 survey online.

Its open search for a contractor is a break with its decision before 2016 to engage IBM without market testing, a move blamed for the bungled online census delivery on August 9-10 that year.

The bureau is yet to announce a preferred bidder.

IBM built online platforms for the census in 2006 and 2011. The bureau chose the company to deliver the online census before 2016 without market testing in a decision later criticised by a federal government review of the shutdown controversy. IBM took on the $9.6 million contract for the project.

Despite funding and staffing pressures, the bureau has told senators it won't outsource the 2021 survey.

It expects more households will complete the next census online, continuing a move way from paper forms beginning more than a decade ago. Households completing the census online will grow from 59 per cent in 2016 and 34 per cent in 2011, if the bureau has predicted correctly.

The shift will increase pressure on the agency to escape the failures leading to its decision to temporarily shut down the survey after IBM alerted it to activity believed to be a possible data breach but later found to pose no threat.

After the "censusfail" Twitter hashtag emerged in response and became a byword for federal government IT blunders, Australian Statistician David Kalisch is pushing back against the widespread view the bureau botched the 2016 survey.

"It really irks me when people still talk about 'censusfail', because it didn't [fail]," Mr Kalisch said.

"It had a glitch, it had a complication around the time of the availability of the online form. But when you look at what the census is supposed to do, in terms of providing high quality data around population, around features of the community, around features of local regions, Australia got all the data that they needed."

A major review into the 2016 shutdown by Malcolm Turnbull's cyber security advisor Alastair MacGibbon warned public mistrust in the census would linger.

"The public’s confidence in the ability of government to deliver took a serious blow, more so than any previous IT failure," Mr MacGibbon's report said.

The MacGibbon report found the bureau's trust in and closeness to IBM were factors leading to the August 9-10 shutdown, and criticised the agency for failing to own up to its mistakes. It found the bureau and the tech company had not adequately planned for a crisis.

Protections were inadequate against the distributed denial of service attacks that brought on the shutdown, despite being part of IBM's brief, Mr MacGibbon said. He called on government agencies to embrace cyber security in upgrading their IT and urged the bureau to improve how it managed tech contracts.

Mr Kalisch said the bureau accepted Mr MacGibbon's findings and had reached similar conclusions in its own investigations. The agency has previously said it had completed the government cyber security chief's recommended reforms.

"With the census, there'd been a history of doing it progressively, iterating the way it was done. But nonetheless the core model was pretty much the same. And within that can come some sense of 'it worked well last time, let's do it again the next time'," Mr Kalisch said.

"One of the things we're particularly mindful of with 2021 is just thinking about some of those past practices can actually not be risk mitigations but actually lead you into the zone of potentially facing greater risks as the environment changes."

Among the old ways that didn't serve the bureau in 2016 was a publicity campaign designed for an earlier era and failing to prepare people for a census moving more decisively away from paper forms. The agency had also mishandled the debate before the survey over its use and retention of data, Mr MacGibbon said.

Mr Kalisch said the bureau had since realised its smaller size compared to other government agencies required it to partner more with others. Its relationships with cyber security agencies inside the federal government were well-established after 2016, he said.

The bureau is speaking to the federal cyber security centre, and electronic spy agency the Australian Signals Directorate, about its protections against attacks.

"I'm not about to disclose some of those treatments or actions, but certainly one of the things that is quite different from last time is that we're being quite proactive in engaging with the cyber security centre and ASD to make sure that as much as possible we specify the treatments that should be in place and also draw upon their expertise that isn't otherwise available in the marketplace."

Mr Kalisch admitted its publicity campaign before the 2016 census didn't reflect one of its innovations, mailing households with an access code for the online form. It would need to communicate differently with the public before 2021.

"It was quite clear when people thought about the change of the census process, there wasn't enough attention to how do we communicate this to the public, and over an extended period of time," he said.

"We're also finding in terms of broader communications, that you do need to think through and actually have the conversation with the community. It's not something you can rush."

The Coalition government is directing in the order of $500 million towards Census 2021, a similar figure to the last survey, when it was expected to save $100 million in the belief that growth in online take-up would reduce costs.

Mr Kalisch said the agency was still working out the next census' costs.

Budget pressures for the bureau include a $36 million shortfall last financial year and it is reviewing its statistical collections.

Its overall budget had been declining, Mr Kalisch said.

"We've been trying to manage all of the risks while still delivering the types of statistics that Australia needs," he said.

"It's really an ongoing challenge but it's one that many agencies are dealing with."

The bureau is getting more critical voices from outside to review its work preparing for the census. Telstra and Tax Office staff sit on its census board, and KPMG is contracted to give advice, Mr Kalisch said.

"It's just a way of making sure the organisation is not blindsided by things taking place in the broader environment that we're not aware of. And really just in the whole approach to decision-making and judgements, the more diverse the group of people you've got involved in the process, the more likely you are to make a better decision," he said.

The bureau has escaped some of the distractions blamed for the troubled lead-up to the 2016 census. Mr Kalisch said there had been no discussion this time of scrapping the five-yearly event. The 2016 federal election closed communication between officials and ministers, and the bureau went a year without an agency chief in 2014.

Australian National University demographer Liz Allen agreed census 2016 was not a failure and called the "censusfail" outcry a "beat-up".

"Australians have embraced the census 2016 data in ways I’ve not seen before," she said.

An unexpected benefit of the controversy was greater public interest and conversation about data, and the bureau had received support from the public to continue its role, Dr Allen said.

The bureau is consulting on its topics for the next survey. Dr Allen said she was heartened by the preparation for census 2021.

"The public consultation about data collection topics and questions is what we’d expect to see from a world class national statistical agency," she said.

"The fact is Australia hasn’t seen a change in the census form, in a substantive way, for around 20 years. This is extraordinary.

"But this is not the fault of the ABS, rather the bureau has been caught up in major funding cuts and been political collateral damage meaning no substantive change to census questions."

Demographer at .id Glenn Capuano said quality data depended on public trust in the bureau.

"The census is really about people having confidence in the privacy and security of data," he said.