An acoustical mesh network is a decentralized communication system that transmits data by using sound to connect computers.
This relatively unknown network type was first used to enable robust underwater communication. More recently, the method has been used in proof-of-concept (POC) trials for acoustical infections as a method of communication among air-gapped computers. Air gapping is an extreme measure used to secure extremely sensitive data against exfiltration.
There are both legitimate and unscrupulous uses for acoustical mesh networks. Hackers can modify software designed for underwater networking to enable air-based and covert communication and use acoustical mesh networks for covert communication with infected systems. Due to their already limited bandwidth (20bits/s), these types of mesh networks commonly use a partial mesh network, in which communication is conducted through the fastest points rather than connecting all endpoints. The networks often use ultrasonic sound outside or at the edge of the range of human hearing. The use of sound beyond the range of human hearing means that malware can stealthily send data without an Internet connection.
POC trials have demonstrated acoustical infections and all elements of the attack have been demonstrated in the real world, strongly suggesting that malware can infect through acoustic channels. BadBIOS, a stealth infection discovered by Dragos Ruiu, is one of the first malwares suspected to create acoustical mesh networks. Ruiu, a security researcher, reported that the malware infected the firmware of the machine, communicating with and comproming other nearby computers through sound.