The amount of covert surveillance by the federal government of welfare cheats has almost halved.
The Department of Human Services spent less than $100,000 on private investigators in 2013-14 to photograph, record or watch 80 alleged Centrelink fraudsters, according to DHS.
Action was taken against 75 of these people, who were tracked at a total cost of $80,000, and a further $10,000 was spent following five people who were not pursued to pay money back.
This was almost half as many as the 143 operations in 2012-13, a quarter as many as the 337 surveillance investigations in 2011-12 and almost seven times fewer than the 566 in 2010-11.
A department spokesperson said the reduction in recent years was primarily because of improvements in other techniques, such as data-matching and data analytics.
The spokesperson said "optical surveillance" methods were used when there were reasonable suspicions of fraudulent activity, serious cases of child support avoidance or income minimisation, when other investigation avenues were inconclusive and surveillance would substantially assist the investigation and when the benefits of using surveillance substantially outweighed the intrusion on the privacy.
It also could include the cost-effective measure of checking a person's publicly available social media accounts to, for example, check whether someone receiving an unemployment benefit was actually working.
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Australian Privacy Foundation board member Roger Clarke said the more intrusion there was into someone's life, the more critical it was that judicial warrants be required.
"There's no doubt DHS should have the ability to do this sort of thing," Dr Clarke said. "There just has to be proportion."
Private investigators who did not want to be named said they were restricted to observing people under surveillance from public places.