Government officials have conceded the performance of their coronavirus contact tracing software is "highly variable" but insist it will still help health authorities.
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More than 5.1 million people have downloaded and registered on the COVIDSafe mobile phone app since it was released.
Over the past week, the tech community has examined the app's code and have identified a number of functional and privacy issues.
Digital Transformation Agency head Randall Brugeaud says the $1.5 million app is being constantly improved.
He conceded its performance on iPhones progressively deteriorates when the device is locked and the app is running in the background.
"There will be circumstances where the app does not capture a Bluetooth handshake," he told a Senate committee hearing on Wednesday.
Nevertheless, he insisted COVIDSafe works, Apple users just had to keep their phones unlocked.
"Within a fortnight or thereabouts - it depends on the timing of the Apple Bluetooth release - the performance will be as good in locked phones as it is in unlocked phones," he said.
Software developer Jim Mussared has discovered problems with the app on Android devices that could potentially leave them open to being tracked for days.
Mr Mussared still recommends most people with Android phones should install the software.
"But if you're in any way in a vulnerable situation for which long-term, multi-day device tracking could be a major threat, do not install the app," he said.
His advice is similar to that given by WESNET, an organisation that offers technology safety advice for domestic violence victims.
It says those whose abusers have sophisticated technical abilities should think about their specific personal circumstances before downloading the app, and suggests if they do install it, they consider leaving their phone behind during any meetings they might want to keep secret.
Mr Brugeaud said his agency was engaging with the tech community on issues relating to the app.
The health department expects to finalise agreements by the end of this week to allow the states and territories to access the contact tracing data.
The prime minister and cabinet colleagues have repeatedly said they want 40 per cent of Australia's 16 million smartphone owners to download COVIDSafe.
But acting secretary Caroline Edwards said the health department had not provided any advice around targets or what percentage of takeup was necessary to lift restrictions on businesses.
"I'll take one, I'll take 10 per cent, I'll take the five million we've got ... and if it gets to 40 per cent and beyond, well, I'll be even more delighted," she said.
About one in 10 smartphones in Australian are too old to use the app, and Greens senator Rachel Siewert pointed out these were most likely to be owned by people most at risk from the virus.
Labor's Murray Watt expressed concern about the link between app downloads and lifting restrictions.
"Here we are two days before that national cabinet meeting with an app that doesn't work all the time, that doesn't necessarily work when iPhones are locked, it doesn't necessarily work when Bluetooth signals are low, it doesn't necessarily work when it's in the background, only half the number of people have downloaded it that the prime minister said was required," he said.
Australian Associated Press
