The success of a mobile app to contact trace Covid-19 cases depends on whether its users can trust their data will be protected, privacy and technology experts say.

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The Ministry of Health plans to make a voluntary app available in the next fortnight to track the movements of people with the virus.

The first version of the app would allow voluntary pre-registration, giving the ministry up-to-date contact details for users.

The ministry was also looking into the use of QR codes to check into businesses or places.

Respecting people's privacy and security would be a key focus, it said.

Privacy Foundation chair Gehan Gunasekara said the app's success would depend on its trustworthiness.

"Trust is the key ingredient here. But if the trust is there and the government has given water tight commitments that it's going to protect the data and only be used for a limited purpose then I think people will entrust their data."

Privacy Commissioner John Edwards said he was confident the government had followed a robust process to ensure that data collected by the app will be used appropriately.

He said he has been working with the Ministry of Health on the project and his office will be keeping an eye on how the data is collected and used.

The app complements, not replaces, manual contact tracing by public health officials, Edwards said.

The associate professor in commercial law at Auckland University said a similar app was said to have had a low uptake in Singapore, so the government needed to be very clear about its purpose and reassure the public about the app's security.

"That's the major concern to make sure the developer or companies are not secretly siphoning data off, we need to be very very clear about that."

Technology commentator Paul Brislen said the details on how the data will be used, how long it would be retained, and who would have access to it still needed clarification.

"If we don't have clarity I suspect Kiwis won't use it."

If the app used Bluetooth technology, it could potentially drain mobile batteries, he said.

"If the app has to be open and running and pinging Bluetooth constantly that will potentially change the way your battery lasts. That might not please some users."

Meanwhile, seven out of 10 adults surveyed by Horizon Research supported the police and health authorities using their personal mobile data to help track and trace those who have been in contact with Covid-19.

In Australia, more than a million people downloaded an official contact tracing app within hours of its release last night.

The Australian app warns users if they have more than 15 minutes of close contact with someone who tests positive.

An audit of New Zealand's contact tracing capabilities by epidemiologist Dr Ayesha Verrall found the country's capacity needed to be increased three- or four-fold as long as the virus remained a health threat.

Dr Verrall said the ministry urgently needed to work on an app to help with contact tracing.

The ministry has been consulting on tracing with the Government Communications Security Bureau (GCSB), New Zealand's communications spy agency, amid growing concern globally that contact tracing could lead to mass surveillance.

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