The Australian census website was shut down by what authorities believe was a series of deliberate attacks from overseas hackers.
Millions of Australians were prevented from taking part in the national survey on Tuesday night.
The Australian Bureau of Statistics (ABS) had boasted only hours before that its website would not crash.
The opposition party is demanding that the minister responsible for managing the census resign.
Every five years, everyone in Australia is required to fill out forms are compiled to provide a snapshot of the country.
Two-thirds of Australians were expected to complete the census online this year, rather than on paper.
Debate about privacy concerns has been raised despite assurances from the government that security would not be compromised.
‘Not an attack’
Assistant Treasurer Michael McCormack, who was responsible for overseeing the census, denied that the national survey was “hacked” or “attacked”.
“It was an attempt to frustrate the collection of data, an attempt to frustrate the collection of data,” he said.
“People should feel rest assured their data is safe.”
The comments contradict earlier comments issued by the ABS which stated that there were four “attacks”.
The opposition party called for Mr McCormack to resign over the website crash.
“There’s few more basic tasks to running a government than conducting a census,” said Andrew Leigh, the assistant shadow treasurer.
“If we don’t get an accurate snapshot on census night, we can’t allocate resources properly.”
The ABS is now working with authorities to determine the source of the “denial of service” attacks.
“The Australian Signals Directorate are investigating, but they did note that it was very difficult to source the attack,” chief statistician David Kalisch told the ABC.
“The scale of the attack, it was quite clear it was malicious.
“Steps have been taken during the night to remedy these issues and I can certainly reassure Australians that the data they provided is safe.”
In the lead-up to the census, crossbench Senator Nick Xenophon’s concerns about privacy were dismissed by the government as “tinfoil hat” politics.
He said it wasn’t clear who should be wearing the hat now.
“Look, there are real concerns,” Mr Xenophon said.
“The census, the ABS, has had five years to get this right.”
After weeks of reminders to “get online August 9”, millions of Australians were frustrated to find they could not complete the survey.
Thousands of people poked fun at the situation on social media with references to the popular television shows including The IT Crowd, The Simpsons and Monty Python.