Labor Assistant Treasurer Andrew Leigh says he's not satisfied with the government's response to the census website 40-hour shutdown.
The online meltdown cost the government $30 million and left thousands of Australians frustrated at their keyboards.
Mr Leigh says it's unclear what oversight procedures were in place.
He's told the ABC it's clear the ministers responsible weren't actively managing the process.
"This was first time where, by default, Australians were expected to go online and fill out the census and ministers don't appear to have taken any responsibility there for making sure that that went well, that the inevitable denial of service attacks that everyone knew would come were buffeted away and appropriate systems put in place."
Australian Bureau of Statistics Chief Statistician David Kalisch says around 40 meetings had been held between the ABS and ministers in the lead-up to August 9, but no concerns had been raised about the bureau's preparedness.
He says the ABS accepts it made mistakes.
"The ABS made a number of poor judgements in our preparation for the census that led to poor service experience by many households and I apologise to the community on behalf of the ABS."
It's been revealed a simple routine test before census night - when the system was hit with four distributed denial-of-service, or DDoS, attacks - could have avoided the lengthy outage.
However, Mr Kalisch says they hadn't anticipated the website would go down.
"We were certainly surprised that the system was vulnerable. We were assured that the system was robust and was ready to go - to a range of different attacks and mechanisms, not just DDoS."
The senate hearing blame trail continued to computer firm IBM, tasked with running the online census.
IBM Managing Director Kerry Purcell has also apologised for the inconvenience, and revealed he's negotiating a deal with the federal government to pay compensation.
But no-one at IBM has been sacked or disciplined.
Mr Purcell says he stands by geo-blocking as an effective D-DoS attack prevention mechanism and has instead pointed the finger at an Internet Service Provider.
"What went wrong? In short the geoblocking protocol was not properly applied by one of the ISPs and this error occurred in circumstances where we had received repeated assurances from the ISP that the protocol was properly in place. That resulted in attack traffic getting through to the e-census site which in turn caused a number of effects that led to IBM's decision to suspend public access to the site. "
The ISP in question? Nextgen.
Senate Committee member Independent Senator Nick Xenophon has told the ABC Nextgen should be given the chance to speak.
"This could happen again, so we need to learn from these mistakes. The mistakes that were made, and I also think that Nextgen, which was basically sledged by IBM, ought to be given the opportunity to give evidence at the senate inquiry."
The Prime Minister's special adviser on cyber security, Alastair MacGibbon, says IBM has to bear responsibility.
He says solely relying on geoblocking to counter attacks clearly failed.
Mr MacGibbon has conducted an internal review into the bungle and his report is currently with the Prime Minister.
Mr Xenophon says it must be made public.
"I think Alistair MacGibbon's report, if it's released as it should be, will be very revealing as to the sequence of events that occurred."
ABS chief David Kalisch has promised a more rigorous approach to the 2021 census.
IBM, the ABS and Mr MacGibbon have all stressed that no personal data was compromised during the incident.
