Contact-tracing apps are akin to submarines, pinging each other directly via Bluetooth as they pass. Each ping contains the unique code for the user. If the user later tests positive for COVID-19, their ID can be broadcast to all other apps. Many privacy experts warn that without clear, legal protections for users, social-graph data could be abused by mass surveillance by governments, as well as hackers and private businesses. Despite their potential, rushing such apps to market may also do more harm than good.”]
Source: https://www.cuinfosecurity.com/blogs/digital-contact-tracing-apps-hype-or-helpful-p-2897