Mobile phone apps aimed at monitoring who has coronavirus and whom they have come into contact with have been launched worldwide, but privacy advocates have concerns.

Three US states, Alabama, North Dakota and South Carolina have signed up to use a contact-tracing app produced by Apple and Google called Exposure Notification

Three US states, Alabama, North Dakota and South Carolina have signed up to use a contact-tracing app produced by Apple and Google called Exposure Notification. The app was released on Wednesday. Several other states and 22 countries, including some in Europe, have also sought to use it, the companies said.

Meanwhile, the app, developed by local governments and not the tech giants, uses Bluetooth technology to inform anyone who was near an infected person for five minutes with an anonymous message. It also urges them to seek medical attention, and is part of software automatically downloaded to iPhones and Android devices.

Speaking about the development, North Dakota Governor Doug Burgum told CNBC: "North Dakota is excited to be among the first states in the nation to utilize the exposure notification app built by Apple and Google to help keep our citizens safe."

But privacy advocates have concerns.

Evan Greer, deputy director of Fight for the Future, a nonprofit digital-rights campaign group said: "As an organization that focuses on privacy and civil liberties, we recognize that contact tracing has been a tool of epidemiology for a long time.

"But we're more concerned about the use of the app, particularly cellphone location data to conduct that kind of contact tracing because that type of information can be so incredibly sensitive and invasive and so easy to abuse."

In a move to reassure the public and privacy campaigners, the tech giants behind the app stress that they will not use much private information. They will, however, allow public health authorities to contact the infected and collect data on their ZIP codes and phone numbers.

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Apple and Google banned developers from using GPS data, which shows someone's location. It also won't allow any government to store data about a person or use the technology without a person's knowledge or consent. Any data collected can't be used for advertising.

'Residents put in danger'

"I think that the proposal that Apple and Google put forth is not perfect but at least preventing the use of GPS data is an important protection there," Greer said.

"So, I think that states that are pushing forward with apps that do collect real-time location data rather than anonymized Bluetooth data, are putting their residents in quite a bit of danger."

It is believed that at least 60 percent of US citizens need to sign up and use the app for it to work.

Over 97,000 people have died of the virus in the US as of Sunday, the largest toll among all the countries in the world, according to a tally kept by the Johns Hopkins University.

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The front page of Sunday's New York Times features the names of 1,000 people who have died of COVID-19 in the US.

"Numbers alone cannot possibly measure the impact of the coronavirus in America, whether it is the number of patients treated, jobs interrupted or lives cut short," the paper said.

Chen Yingqun in Beijing, Xinhua and agencies contributed to this story.