The submission was listed, along with 37 others, on the official site after submissions to the inquiry closed on 21 September.
In the submission, the ABS laid the blame for the census fiasco squarely at the feet of IBM.
The census was held on 9 August but the website was taken offline at 7.30pm with a distributed denial of service being blamed.
It claims that after a fourth "attack" at 7.28pm, the system became unavailable to the public.
This attack was inferred as being from overseas but when technicians tried to isolate the website using geoblocking the measure did not work.
"The online census system was hosted by IBM under contract to the ABS and the DDoS attack should not have been able to disrupt the system. Despite extensive planning and preparation by the ABS for the 2016 census this risk was not adequately addressed by IBM and the ABS will be more comprehensive in its management of risk in the future," the submission says.
The ABS has blamed the media for the unexpected volume of calls it received in the run-up to the census, saying that this was due to a "focus on potential of census fines creating a degree of public fear".