The Australian Bureau of Statistics (ABS) has targeted service provider IBM in its submission to a Senate inquiry into the handling of the botched census.

Key points: Thousands of Australians were prevented from taking part in census last month

Thousands of Australians were prevented from taking part in census last month Senate inquiry to look into preparation, administration and management of census

Senate inquiry to look into preparation, administration and management of census Malcolm Turnbull has forecast possible sackings over "failure"

Thousands of Australians were prevented from taking part in the census last month after the site was pulled down due to numerous attempted denial of service attacks, which overload a website by simulating lots of users trying to access the site at the same time.

In the fallout that followed, a Senate inquiry was established to look into the preparation, administration and management of the 2016 census by the ABS, which published its submission today.

The 123-page document emphasised the security measures promised by IBM, stating that the service provider's contract ensured it would mitigate the risk of distributed denial of service (DDoS) attacks.

"During 2016, the ABS had sought and received various assurances from IBM about operational preparedness and resilience to DDoS attacks," it stated.

"At no time was the ABS offered or advised of additional DDoS protections that could be put into place.

"Additionally, no suggestion was made to the ABS that the DDoS protections that were planned were inadequate."

The ABS submission also stated that the DDoS protection systems were not independently tested, regardless of the assurances given by IBM.

The submission also criticised the media for its coverage of the census, saying the ABS was rarely approached for comment regarding stories on privacy.

"The ABS is aware of a number of instances where the community benefit of what the ABS was proposing to deliver from the 2016 census was not able to get a reasonable representation in the media," it stated.

The ABS said that so far there had been around half as many refusals to answer the survey in 2011, despite a campaign to boycott the census because of privacy concerns.

The question that had the highest rate of refusal was about religion.

'This has been a failure of the ABS'

The submission also outlined issued with its communications on the night of the census, saying that more than two million calls from the public went unanswered.

The ABS had expected 1.6 million calls — a number they conceded they could not handle — and instead received 3.2 million. Around 1.1 million were answered.

The ABS also reported receiving four times the amount of online enquiries compared to 2011, at a total of 400,000 submissions.

Speaking after the census evening, Prime Minister Malcolm Turnbull forecast possible sackings.

Mr Turnbull told reporters last month that "which heads roll, where and when, will be determined once the review is complete".

"I made it very, very clear that what we needed to do was be absolutely straight and frank with the Australian people," he said.

"This has been a failure of the ABS."

The Prime Minister's Special Adviser on Cyber Security, Alastair MacGibbon, also provided a small addition to the timeline of events on August 9.

The website was shut down after the fourth attack and, as Mr MacGibbon wrote in his submission, "a monitoring system indicated that there was outbound traffic from the eCensus system, and the fear was it was potentially malicious".