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 social data, social-graph data could be abused by governments, as well as by hackers. Australia, India and UK Pursuing Centralized Approach Many Privacy Experts Warn Against Such Apps.”]
Source: https://www.govinfosecurity.com/blogs/digital-contact-tracing-apps-hype-or-helpful-p-2897