ArsTechnica explains about a malware that they have named "badBios" which was supposedly able to infect other computers via high ultrasound frequencies.
I find this, not an impossibility by itself, but my guess is that this only would be possible in the case that the computers had some type of sound processing software that got to process the sound and was programmed precisely to interpret that sound for causing malware effects.
But what I'm skeptic about is that it was only achieved by that sound emission and reception, without that additional software.
Did such a malware (with only that emission and reception) exist?
PD: There's also some extra explanation here. There it clearly states its done by sound transmission.