Dolphin Attack Affects Siri and Alexa

Source: youtube.com

Researchers at Zhejiang University have published a white paper detailing how they were able to attach devices using a inaudible frequency. The DolphinAttack uses ultrasonic frequencies to access speech recognition systems like Siri, Cortana or Alexa.

All these systems are voice controllable systems (VCS) that have a micro electro mechanical system microphone that vibrates in response to air pressure changes caused by sound waves. These microphones can detect frequencies above the audible range of human hearing (20,000 Hz).

Sound has an unusual property called subharmonics. These are frequencies that are generated by the fundamental frequency and are a fractional ratio to the fundamental. These are generated at a lower amplitude than the fundamental so they are not audible but there is enough energy to cause the microphone to pick up the vibration.

Source: twitter.com

By sending a signal that is a multiple of the frequency required to activate the VCS but is beyond the 20,000 Hz hearing threshold, a hacker can activate the device without an audible sound. This is how the DolphinAttack works.
Source: rt.com