The Australian Bureau of Statistics shut down the website after a series of denial-of-service attacks on Tuesday night, with the strongest one coming just after 7.30pm (AEST).
"This was not an attack, nor was it a hack but rather, it was an attempt to frustrate the collection of Bureau of Statistics census data," minister Michael McCormack told reporters in Canberra on Wednesday.
The Bureau of Statistics decided to shut down the census form to safeguard and protect data already submitted, the minister said.
There was a large-scale denial-of-service attack on the website, which is when the site is flooded with requests for information and the servers are overwhelmed - as if a huge crowd of people tried to get through a doorway all at the same time.
"Following, and because of this, there was a hardware failure," Mr McCormack said, saying the ABS took a very cautious approach in shutting down the site.
'It was an attack'
Earlier, the Australian Bureau of Statistics said the census website was shut down after being attacked by foreign hackers.
"It was an attack," chief statistician David Kalisch told ABC radio on Wednesday.
"It was quite clear it was malicious."
The ABS is now working with the Australian Signals Directorate to determine the source of the attack.
Mr Kalisch said so far it had been very difficult to work out where it came from.
A number of digital assaults on the census website began during the day on Tuesday and were repelled.
But the frequency increased as the evening neared and many Australians trying to reach the census site after 7pm couldn't connect.
It was at this point the ABS said it began the process of shutting down the site.
Mr Kalisch said he believed the details of people - including Prime Minister Malcolm Turnbull - who had managed to successfully access the site were secure.
"I can certainly reassure Australians the data they provided is safe," he said.
The ABS released a statement around 11.30pm on Tuesday advising the websites was unavailable.
It's reassured Australians they won't be fined for not completing the census on Tuesday.
Mr Kalisch said he expected the site would be back on line around 9am on Wednesday.
Mr Kalisch and the minister in charge of the Census, Michael McCormack, will hold a press conference in Canberra later on Wednesday.
Labor calls for census minister to resign
Labor wants the minister responsible for the botched census, Michael McCormack, to resign and believes a re-run is not out of the question.
Shadow assistant treasurer Andrew Leigh is furious the government failed to properly explain its decision to take the national survey online, where it was then subject to foreign cyber attacks on Tuesday night.
"If you can't get the census right how can you govern the country," he told ABC radio on Wednesday.
Dr Leigh criticised the coalition for leaving the position of chief statistician vacant for a year and feared it would now blame the bureaucrats.
"What I'm concerned about is that the government is going to pass the buck," he said.
Dr Leigh urged people to hop online as soon as the website is working again.
Crashing halt
Australia's first online census came to a crashing halt after the Australian Bureau of Statistics website went down completely on Tuesday night.
Many people began experiencing difficulties in the late afternoon, despite more than 1.3 million having successfully completed the Australian Bureau of Statistics' online form, until the site crashed completely around 7.30pm.
Those experiencing error messages and other issues with the website took to social media to complain.
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人口普查夜 数名议员拒绝填报姓名以示抗议
