Covert channels can be used to circumvent system and network policies by establishing communications that have not been considered in the design of the computing system. We construct a covert channel between different computing systems that utilizes audio modulation demodulation to exchange data between the computing systems over the air medium. 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 utilizing the ultrasonic frequency range. 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. A covert acoustical mesh network can be conceived as a meshed botnet or malnet that is accessible via inaudible audio transmissions. Different applications of covert acoustical mesh networks are presented, including the use for remote keylogging over multiple hops. It is shown that the concept of a covert acoustical mesh network renders many conventional security concepts useless, as acoustical communications are usually not considered. Finally, countermeasures against covert acoustical mesh networks are discussed, including the use of lowpass filtering in computing systems and a host-based intrusion detection system for analyzing audio input and output in order to detect any irregularities.
@cite_0: The powerful processors and variety of sensors in new and planned mobile Internet devices, such as Apple’s iPhone and Android-based smartphones, can be leveraged to build cyber-physical applications that collect sensor data from the real world and communicate it back to Internet services for processing and aggregation. This article presents key R&D challenges facing developers of mobile cyber-physical applications that integrate with Internet services and summarizes emerging solutions to address these challenges. For example, application software should be architected to conserve power, which motivates R&D on tools that can predict the power consumption characteristics of mobile software architectures. Other R&D challenges involve the relative paucity of work on software and sensor data collection architectures that cater to the powerful capabilities and cyber-physical aspects of mobile Internet devices, which motivates R&D on architectures tailored to the latest mobile Internet devices.
@cite_9: Malware targeting mobile phones is being studied with increasing interest by the research community. While such attention has previously focused on viruses and worms, many of which use near-field communications in order to propagate, none have investigated whether more complex malware such as bot-nets can effectively operate in this environment. In this paper, we investigate the challenges of constructing and maintaining mobile phone-based botnets communicating nearly exclusively via Bluetooth. Through extensive large-scale simulation based on publicly available Bluetooth traces, we demonstrate that such a malicious infrastructure is possible in many areas due to the largely repetitive nature of human daily routines. In particular, we demonstrate that command and control messages can propagate to approximately 2 3 of infected nodes within 24 hours of being issued by the botmaster. We then explore how traditional defense mechanisms can be modified to take advantage of the same information to more effectively mitigate such systems. In so doing, we demonstrate that mobile phone-based botnets are a realistic threat and that defensive strategies should be modified to consider them.
@cite_18: 
As @cite_0 pointed out, mobile cyber-physical system applications might be present on common sensory devices (e.g., on smartphones). Malware infected devices might be connected to form a botnet (as described by Dagon, Gu and Lee @cite_18 ). With smartphones and similar devices, such a botnet might be built upon one of many network interfaces present in such devices and even on input and output sensors as we describe in this article, although we do not specifically experiment with smartphones and focus at interconnecting laptops. A near-field communication botnet approach based on bluetooth is presented by Singh, Jain, Traynor and Lee @cite_9 . We, instead, use audio communications for our botnet-like approach in near-field communications to construct a covert acoustical mesh network consisting of malware infected drones.