Wikipedia
BadBIOS is an alleged advanced persistent threat reported by network security researcher Dragos Ruiu in October 2013 with the ability to communicate between instances of itself across air gaps using ultrasonic communication between a computer's speakers and microphone. To date, there have been no proven occurrences of this malware.
Ruiu claims the virus is able to infect the BIOS of Windows, Mac OS X, BSD and Linux as well as spread infection over USB flash drives. Rob Graham of Errata Security produced a detailed analysis of each element of the claims about BadBIOS's capabilities describing the software as "plausible", whereas Paul Ducklin on the Sophos Naked Security blog suggested "It's possible, of course, that this is an elaborate hoax". After Ruiu posted data dumps which supposedly demonstrated the existence of the virus, "all signs of maliciousness were found to be normal and expected data".
In December 2013 computer scientists Michael Hanspach and Michael Goetz released a paper to the Journal of Communication demonstrating the possibility of an acoustic mesh networking at a slow 20 bits per second using a set of speakers and microphones for ultrasonic communication in a fashion similar to BadBIOS's described abilities.