German researchers have developed a new computer virus that can capture secret information from a PC and take over the soundcard to transmit the data to a close by machine as a high-frequency sound through air inaudible to human beings.
Researchers at Fraunhofer Institute for Communication, Information Processing and Ergonomics were able to broadcast passwords and other information at a rate of 20 bits per second over a 20 metre distance.
Researchers said that the underlying network stack is based on a communication system that was originally designed for robust underwater communication.
"We adapt the communication system to implement covert and stealthy communications by utilising the near ultrasonic frequency range," they added.
"We further demonstrate how the scenario of covert acoustical communication over the air medium can be extended to multi-hop communications and even to wireless mesh networks.
"If we want to exploit a rigorously hardened and tested type of computing system or networks of this type of computing system, we have to break new ground."
As part of the experiment, researchers used five Lenovo T400 laptops powered by Debian 7.1, while built-in speakers and microphones of computers were used to transmit passwords and other information.
"Alongside keystroke information it would also be possible to forward other security critical data such as private encryption keys or small-sized text files with classified information from the infected victim to the covert network," researchers added.
"This data could be sent out periodically to maximise the likelihood of data extraction from the host and it could also be spread to different environments when the computing system is carried around."
The authors demonstrated that setting up secret acoustical mesh networks in air is possible in setups with normally available business laptops.