A smartphone app to alert people who may have come into contact with a COVID-19 sufferer is to be rolled out in the UK but there are worries over privacy breaches. 

Contact-tracing involves sending signals between mobile phones, often using Bluetooth technology, and has already been implemented in countries such as South Korea and Singapore.

Users will voluntarily report any positive infections and symptoms via the app, which then sends "anonymous" alerts to other users that person may have come into close contact with.

But there are concerns over the privacy of data that will be generated and whether or not enough people will use the app for it to be effective.

On 12 April, the UK's health secretary, Matt Hancock, said the NHS was working with the "world's leading tech companies" to develop the app.

"All data will be handled according to the highest and ethical security standards and would only be used for NHS care and research," he said. 'We won't hold it any longer than it's needed and as part of our commitment to transparency we'll be publishing the source code, too."

Ross Anderson, a professor of security engineering at the University of Cambridge and one of the UK's leading cyber-security experts, has his doubts about whether the government can ensure the privacy of data.

"I've been involved in safety and privacy of healthcare IT off and on for 25 years and even if you go all the way back to the 1990s and the peak of the HIV epidemic, the problem we have with our public health people is that they kept as much data as they could and they kept it forever," said Anderson.

A group of nearly 300 experts from 26 countries have also written to the UK government warning that not enough people will use the app if privacy isn't ensured. The technology must not "enable unwarranted discrimination and surveillance," the letter stated.

Experts say around 60 percent of the population would need to use the app for the measure to be effective and that figure involves 80 percent of smartphone users.

Contact-tracing is crucial for countries to end lockdowns, as it identifies who has had the disease.

Without sufficient testing, the UK's efforts could depend on self-reporting but this also raises the other concern about the reliability of the data. The UK's National Health Service is reportedly testing the app in the north of England this week before it's rolled out nationwide in the coming weeks.

Aside from the logistical hurdles, ensuring privacy will be a key test if it is to prove successful.