As Predicted – NHS Track and Trace Leaves Personal Data Vulnerable Recently, an ex GCHQ employee warned the public against using public Wi-Fi networks with the NHS track and trace app. So how does track and trace work, what problems have been discovered with the technology, and why is it a bad idea? How does track and trace work? Trying to stop the spread of COVID around the world has been a challenge for all nations. Some nations, such as New Zealand, have been privileged with being an island nation that can completely shut their borders. Other nations, such as the UK, are not as fortunate with a much larger population and increased importance worldwide.