A team from Ruhr-Universität Bochum has succeeded in integrating secret commands for the Kaldi speech recognition system – which is believed to be contained in Amazon’s Alexa and many other systems – into audio files. These are not audible to the human ear, but Kaldi reacts to them. The researchers showed that they could hide any sentence they liked in different types of audio signals, such as speech, birds’ twittering, or music, and that Kaldi understood them. The results were published on the Internet by the group involving Lea Schönherr, Professor Dorothea Kolossa, and Professor Thorsten Holz from the Horst Görtz Institute for IT Security (https://adversarial-attacks.net/).