Scientists create malware that communicates using sound, no network required
 

Straight from camp "what could go wrong" scientists at the Fraunhofer Institute for Communication have developed a proof-of-concept malware that can communicate with other machines nearby, using just standard laptop speakers and microphones. Most importantly, the computers don't need to be on the same -- or technically any -- network, they just need to be within 65 feet of each other. Even more sinister, is the fact that the researchers who developed the method claim they can form audio "mesh" networks to extend this reach much farther.

http://www.engadget.com/2013/12/03/audio-malware/