Authorities Are Blaming Foreign Hackers For The Census Meltdown

"It was an attack, and we believe from overseas."

The Australian Bureau of Statistics is blaming four attacks from "overseas" hackers for its website repeatedly crashing on millions of people during the census.

Alan Porritt / AAPIMAGE

People were left unable to access the online census Tuesday night, with just two million forms collected before the site was shut down completely.

The ABS' David Kalisch told ABC's AM the agency believed its system was repeatedly attacked from overseas hackers.

"It was an attack, and we believe from overseas," he said.

When pushed on whether the ABS thought it was a deliberate act of foreign sabotage, Kalisch said, "we believe so".

According to the ABS, the website was attacked four separate times and the census was taken offline shortly after 7:30pm AEST after the fourth attack.

"The Australian Signals Directorate are investigating, but they did note that it was very difficult to source the attack," said Kalisch.