SYDNEY (Reuters) - Australia’s national census, which provides a snapshot every five years of the country’s people, from religion to income, has become an unlikely flashpoint over privacy concerns.

Australians are being asked to fill in a host of details about themselves online for the first time in the 105-year history of the census, leading some politicians and privacy advocates to partially boycott the survey.

The Australian Bureau of Statistics (ABS) said the information gathered is important because it helps set public policy.

The census covers every inhabited corner of Australia’s 7.7 million square km (3 million square mile) landmass, as well as 8,600 islands, the bureau said.

But worries over data security and changes to the way names and addresses are collected and retained - they will now be held for four years rather than 18 months - have privacy advocates concerned.

“Rather than being a snapshot of the nation, this census will now morph into a mobile CCTV that follows every Australian,” Senator Nick Xenophon said in a statement.

“The ABS has failed to make a compelling case why names must be provided, and stored for four years.”

He has support from across the left, centrist and right-wing minor parties elected to parliament in a recent general election.

Bill McClennan, Australia’s chief statistician from 1995 to 2000, said the retention of names was “the most significant invasion of privacy ever perpetrated on Australians by the ABS”.

Cabinet minister Christopher Pyne dismissed such fears as far-fetched.

Nevertheless, Xenophon and three fellow senators have said they will not write their names on the census forms, on pain of an A$180-per-day fine.

Names and addresses have always been part of census questionnaires and improve the quality of the data, allowing better public policy, Australia’s head statistician, David Kalisch, told reporters on Tuesday.

“The ABS shares the same concern about your privacy as privacy advocates and has an unblemished record of keeping census data safe,” he said.

The data will be collected from Tuesday. People have until Sept. 23 to fill in the forms and the data will then be crunched by 38,000 staff. Findings will be published from April.