Guarantees that Singaporean phone data would only be used to fight COVID-19 were hollow. At the beginning of the coronavirus pandemic, the country's response was hailed as one of the most effective around the world. Aided by government-backed technology and a private venture, Singaporeans were offered tools that could help track the spread of the virus effectively. However, their use came at a price: their private data, and most worryingly, the implications could stretch beyond the country’s borders. Kirsten Han investigates in MIT Technology Review.