Okay, so because he could not remove the audio interface, is MUST was the only logical infection vector remaining? That is a very strong claim, particularly since I do not see any claims that he is also HEARING the requisit very long and loud screeching sounds that would imply. Audio data transmissions on consumer grade devices unavoidably involve sound, right?
Well that is the thing, if it were pitched high enough then no, you probably wouldn't hear it. (that is also beneficial for higher speed transfers).
What the article said was that he was seeing packets from the airgapped host (that means nothing but air around it, no wifi) which stopped when he disabled the speaker and microphone. That suggested that this was the 'wire' between the two.
One of the side effects of using peizo electric speakers (which are nice and flat so adored by mobile device makers and laptop makers alike) is that they often have frequency response ranges above 20khz. Many people cannot hear frequencies over 15Khz, although 15Hkz (which was the scan rate of CRT monitors) can be heard by some folks and poorly wound flyback transformers would drive them nuts.
> poorly wound flyback transformers would drive them nuts
Those and marginal capacitors do drive us nuts. And that's one reason such communication wouldn't have to be completely out of human hearing range. Those of us who can hear it aren't going to be shocked by yet another high-pitched whine in a room full of electronics.
I considered this before posting. If it was near ultrasonic it would have near zero chance of useful transmission unless the attacker and victim were very particularly aligned. The higher the sound frequency, the less sound curves around obstacles.
