In 2015, the Volkswagen emissions scandal involved revelations that Volkswagen AG had deliberately falsified emission reports by programming engine management unit firmware to detect test conditions, and change emissions controls when under test. The cars thus passed the test, but in real world conditions, emitted up to forty times more emissions than allowed by law. An independent report in September 2015 warned that this extended to "every major car manufacturer", with BMW, and Opel named alongside Volkswagen and its sister company Audi as "the worst culprits", and that approximately 90% of diesel cars "breach emissions regulations". Overlooking the direct responsibility of the companies involved, the authors blamed the violations on a number of factors, including "unrealistic test conditions, a lack of transparency and a number of loopholes in testing protocols".