In 2016, the US Federal Trade Coimmission issued a warning to app developers that had installed Silverpush, software that uses device microphones to listen for audio signals inaudible to the human ear that identify the television programmes they are watching. Nonetheless, similar technology continued to spread. In 2017, software from the TV data collection startup Alphonso, began to spread. As many as 1,000 gaming, messaging, and social apps using Alphonso's software, some of them aimed at…