For the purposes of this article, it is assumed the air-gapped computer is already running the malware, having been infected by some other means (ex. thumbdrive). The ultrasound communications provide a continuous (albeit slow) link between two infected computers.

It would be quite impressive, though, if a vulnerability in an audio driver allowed an uninfected computer to be infected simply by "hearing" the exploit sound!

That would present infection vector^^. Study was purely about two computers with very special software trying to covertly communicate using ultrasound.