Computers Can Be Hacked Using High-Frequency Sound

Using the microphones and speakers that come standard in many of today's laptop computers and mobile devices, hackers can secretly transmit and receive data using high-frequency audio signals that are mostly inaudible to human ears, a new study shows.

Michael Hanspach and Michael Goetz, researchers at Germany's Fraunhofer Institute for Communication, Information Processing, and Ergonomics, recently performed a proof-of-concept experiment that showed that "covert acoustical networking," a technique which had been hypothesized but considered improbable by most experts, is indeed possible.
http://www.scientificamerican.com/article.cfm?id=computers-can-be-hacke…
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In their experiments, Hanspach and Goetz were able to transmit small packets of data between two air-gapped Lenovo business laptops separated by distances of up to about 65 feet (20 meters). Moreover, by chaining additional devices that picked up the audio signal and repeated it to other nearby devices, the researchers were able to create a "mesh network" that relayed the data across much greater distances. Importantly, the researchers were able to emit and record the ultrasonic and near-ultrasonic frequencies, which cannot be detected by humans, using the sound processor, speakers and microphone that came standard with the laptops.