Computer scientists have developed a malware prototype that uses inaudible audio signals to communicate, a capability that allows the malware to covertly transmit keystrokes and other sensitive data even when infected machines have no network connection. The proof-of-concept software—or malicious trojans that adopt the same high-frequency communication methods—could prove especially adept in penetrating highly sensitive environments that routinely place an “air gap” between computers and the outside world. Using nothing more than the built-in microphones and speakers of standard computers, the researchers were able to transmit passwords and other small amounts of data from distances of almost 65 feet. The software can transfer data at much greater distances by employing an acoustical mesh network made up of attacker-controlled devices that repeat the audio signals.