Thousands of Australians trying to complete the compulsory the census last night were met with an error message.
The Australian Bureau of Statistics (ABS) said this morning the error was as a result of hackers trying to sabotage the survey, ABC News reports.
ABS's David Kalisch said after the fourth attack from Hackers, they had no choice but to shut the website down.
'It was an attack, and we believe from overseas,' he said.
Kalisch added: 'The Australian Signals Directorate are investigating, but they did note that it was very difficult to source the attack.
'It was quite clear it was malicious.'
The website was shut down just after 7.30 p.m to 'ensure the integrity of the data'.
'The first three caused minor disruption, but more than 2 million forms were successfully submitted and safely stored.
'Steps have been taken during the night to remedy these issues and I can certainly reassure Australians that the data they provided is safe.'
This is the firs time that the census survey has gone digital.