In September 2015, the German Volkswagen Group, the world’s largest car producer, admitted to having installed “defeat devices” in 11 million diesel cars sold worldwide between 2008 and 2015. The devices were designed to detect and adapt to laboratory tests, making the cars appear to comply with environmental standards when, in fact, they emitted pollutants called nitric oxides, or NOx, at levels that were on average four times the applicable European test-stand limit.