This Ars Technica story of some malware that can transmit itself even when all the obvious transmission vehicles (power, Bluetooth, Wifi) has been removed is mind-boggling:
Ruiu said he arrived at the theory about badBIOS’s high-frequency networking capability after observing encrypted data packets being sent to and from an infected machine that had no obvious network connection with—but was in close proximity to—another badBIOS-infected computer. The packets were transmitted even when one of the machines had its Wi-Fi and Bluetooth cards removed. Ruiu also disconnected the machine’s power cord to rule out the possibility it was receiving signals over the electrical connection. Even then, forensic tools showed the packets continued to flow over the airgapped machine. Then, when Ruiu removed internal speaker and microphone connected to the airgapped machine, the packets suddenly stopped. With the speakers and mic intact, Ruiu said, the isolated computer seemed to be using the high-frequency connection to maintain the integrity of the badBIOS infection as he worked to dismantle software components the malware relied on.