An anonymous reader writes "Researchers at Fraunhofer FKIE, Germany have presented a paper on covert acoustical communications between laptop computers. In their paper 'On Covert Acoustical Mesh Networks in Air', they describe how acoustical communication can be used to secretly bridge air gaps between computers and connect computers and networks that are thought to be completely isolated from each other. By using ad-hoc routing protocols, they are able to build up a complete mesh network of infected computers that leaks data over multiple hops. A multi-hop acoustical keylogger is also presented where keystrokes are forwarded to an attacker over multiple hops between different office rooms. The fundamental part of the communication system is a piece of software that has originally been developed for acoustic underwater communications. The researchers also provide different countermeasures against malicious participation in a covert acoustical network. The limitations of air gaps have been discussed recently in the context of a highly advanced malware, although reports on this so-called badBIOS malware could not yet be confirmed."