In 2015, hacker group Anonymous stole massive amounts of data from the US Census Bureau servers.

This year, the Australian Bureau of Statistics [ABS] expects two thirds of people to fill out the survey online - and it could be the target of a similar attack.

When Anonymous hacked the US Census Bureau, they leaked the material they took online, including usernames, email addresses and office phone numbers of the organisation's more than 4,000 staff, The Register reported.

Online security experts fear an attack could be far worse in Australia if hackers target the Census website and personal information to use for malicious purposes like identity theft.

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The 2016 Census will provide a 'snapshot' of the country on the night of Tuesday, August 9

Two thirds of Census 2016 forms are expected to be completed online and major concerns are held that the website and Census information will be targeted by hackers

The US Census Bureau was hacked in 2015 and a hack on the Australian Bureau of Statistics Census website could be worse

The US Bureau of the Census was hacked last year

Security experts have already raised concerns about the safety of the online system for completing the Census, including that some of its protection is out of date and easy to hack.

Daemon Singer, treasurer for Electronic Frontiers Australia [EFA], a non-profit promoting digital freedom, access and privacy, told Daily Mail Australia the data would be a 'honeypot' for hackers.

'It will be sitting there and people will look at it and think what can we sell that for? The answer is billions.'

He told The Australian targeting the Census would provide hackers with the details the needed for identity theft on a massive scale.

And despite the ABS' reassurances their website has the capacity to support the millions of people completing the Census on Tuesday night, experts have warned hackers may target it.

Senior information lecturer Dr Ernest Foo

Senior information lecturer Dr Ernest Foo told The Daily Telegraph it was possible the website was target for hackers.

Internet activists could overwhelm the site with so much digital traffic it would shut down, he said.

He told Daily Mail Australia information was more valuable now and with it all in one place.

There has been nationwide concern about this year's Census.

Politicians, privacy and security experts and the public are furious about the lack of choice about providing names and addresses in the Census, and the extended retention of personal data by the ABS in order to create 'new products'.

The ABS has tested its online Census site for its capacity to deal with large numbers using it on Tuesday night, and it expects it to handle them without problems.

Supplying false information on a Census form comes with an $1800 fine and late fees - from mid-September onwards - incur a $180 fine each day.

Census night is Tuesday, August 9.