The Australian census website was shut down by what authorities said 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 prime minister assured the public that their personal information was not compromised.
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.
