The UK will trial its controversial contact-tracing app today on an island of 141,000 people — and it wants more than 50% to download it

• The UK will trial its contact-tracing app on the Isle of Wight this week.
• The app will automatically alert users if they've been in the proximity of another app-user who has self-reported for having coronavirus.
• The app has caused some concern amongst privacy and cybersecurity experts as the UK has taken the decision to centralize user data — a move which some experts worry could be a route to mass surveillance.
• Visit Business Insider's homepage for more stories.

The UK is getting ready to trial its contact-tracing app today by launching it on a small island off the south coast of England.

"This week we will be piloting new test, track and trace procedures on the Isle of Wight with a view to having that in place more widely later this month," cabinet minister Michael Gove said in a press briefing on Sunday.

Gove added that said the government is aiming for more than half of the 80,000 households on the Isle of Wight to download and use the app.

The way the UK app will work is that if a user is diagnosed with coronavirus or develops symptoms, they will report themselves in the app — which will then send an automatic alert to all the other users that user has been in proximity with for the last two weeks. The app keeps a log of which phones have been near each other using Bluetooth.

The UK government has been advised by experts that roughly 56% of the UK population — meaning 80% of smartphone users — would have to download and use the app for it to have a meaningful effect in slowing the spread of the virus.

Medical director for NHS England Stephen Powis cautioned that even if the testing goes well, the app will not be a panacea.

"It is likely to be one component of a number of measures that will be needed. I think it's unlikely that on its own it is going to be the single measure or the single intervention that will ensure that the virus is always under control," Powis said.

He added that it will need to be complemented by manual contact-tracing — employing real humans to contact people diagnosed with COVID-19 and work out who they may have been in contact with. UK Health Secretary Matt Hancock previously said the government aims to hire 18,000 human contact-tracers.

The UK government has also taken the system to reject a specialized contact-tracing API developed by Apple and Google. The decision hinged on a disagreement over privacy. Apple and Google stipulate that to use their API, governments must de-centralize the processing of users' data, meaning it stays on their phones. The UK has opted to centralize the data on an external server, meaning it can be collected and studied more easily.

This has raised concerns among privacy and cybersecurity experts, and last week 170 experts signed an open letter to the government calling for appropriate safeguards to make sure the app isn't used for mass surveillance.

Eerke Boiten, a cybersecurity expert at De Montfort University told Business Insider in April that a lack of transparency around exactly how the app will work also raises legal questions. In particular, he is worried that the UK government does not seem to have conducted a data impact assessment.

"They've got the right message but they're not providing the actual transparency they want to be providing," he said. "The main thing is conducting a data protection impact assessment, which they are legally required to do anyway.

"This falls within the conditions for data protection impact assessments, it's large-scale monitoring of sensitive data. It should have been done a long time ago, should have been started a long time ago, there should be living documents that develop alongside the process."

On Sunday, a group of lawyers drafted a legal opinion that likewise calls on the government to justify its centralized approach.

"[A] centralized smartphone system – which is the current UK Government proposal – is a greater interference with fundamental rights and would require significantly greater justification to be lawful. That justification has not yet been forthcoming," they wrote.