It is billed as the night the nation pauses but could it also be the night that breaks the country's internet?

The Click Frenzy meltdown of 2012 all over again?

Census Australia 2016 is upon us but this time the biggest peacetime logistical operation in the country is going digital - en masse.

More than 15 million people are expected to flood the Census site over the course of Tuesday to complete their forms and fears have been raised the great snapshot of 2016 might be end up being the great digital failure of 2016.

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Not possible, Australian Bureau of Statistics' Census boss Chris Libreri told news.com.au.

He said the system had passed testing with flying colours, so was unlikely to repeat the much-hyped failure of the 2012 Click Frenzy "sale that stops a nation" that only sent servers into meltdown.

"We have load tested it at 150 per cent of the number of people we think are going to be on it on Tuesday for eight hours straight and it didn't look like flinching," he said.

"We wouldn't do it unless we were able to safely do it, we have evolved it and we are confident."

Libreri said the expectation was that 65 per cent of Australians, or nearly 16 million, would complete their Census online this year.

He pointed out that while this year was the first time it was widely promoted as digital, it was not actually the first time there was the option to complete it digitally.

He said 30 per cent of respondents in 2011 completed their forms online, while about 10 per cent did so back in 2006.

Even back in the relative dark ages on the internet, 2001, a very small percentage of people completed it online.

"It is a misnomer that this is the first year we have gone digital, we have been experimenting since 2001," he said. "It's the same system, we have just kept evolving it, and we have not had a problem at all with it, it has never even quivered.

"We have designed the thing to be very simple, very lightweight and secure, it doesn't take up a lot of space, so it basically flies through."

While Libreri regards the chance of a total system crash as unlikely, in the event it does, people have been advised not to panic.

People have until September 23 to complete their forms online or in paper form, before fines are issued.

We have designed the thing to be very simple, very lightweight and secure, it doesn't take up a lot of space, so it basically flies through.

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Field officers will begin knocking on doors of those who have not completed their forms from two weeks after Census night.

Fines will only be issued to those who refuse to participate, not to those who forget.

In relation to security concerns, particularly hackers with the first large scale online Census, Libreri moved to allay concerns there too.

"It is a very unlikely event, we don't have any present threats," he said.

"We have been planning this a long time. Our systems are as strong as we can possibly make them and we have done it before.

"We know it's a badge of honour for hackers, you know, so we actually do employ our own hackers, we employ ethical hackers to test the system."

As for the rampant privacy concerns being expressed this Census, given it is the first where filling in a name is not optional, Mr Libreri said the concerns were not new.

Privacy is a big concern for Australians, and that's something we deal with every single day.

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"98 per cent of people did the Census in 2011 and if you Google 2011 Census privacy you'll see many similar comment as we are seeing now," he said.

"Privacy is a big concern for Australians, and that's something we deal with every single day.

"We do household surveys every month, so we are well aware of concerns about privacy."

The ABS says names will be held separately to form replies, and they will never be recombined.

Records will be destroyed after four years.

In the unlikely event the system does meltdown on Tuesday night, concerned people who already have their forms can always complete it early, or wait until after the date.

Access codes that have been posted will remain valid until September 23.

On Friday, Libreri said 200,000 households had already opted to submit their forms early.