THERE ARE NASTY CRITTERS OUT THERE. BadBIOS is one of ‘em, according to Dan Goodwin at ArsTechnica, who has an article you should read, “Meet “badBIOS,” the mysterious Mac and PC malware that jumps airgaps”. Jumps airgaps? This is truly dangerous.
"We had an air-gapped computer that just had its [firmware] BIOS reflashed, a fresh disk drive installed, and zero data on it, installed from a Windows system CD," Ruiu said. "At one point, we were editing some of the components and our registry editor got disabled. It was like: wait a minute, how can that happen? How can the machine react and attack the software that we're using to attack it? This is an air-gapped machine and all of a sudden the search function in the registry editor stopped working when we were using it to search for their keys."
It seems that even your speakers can pass on the nastiness:
For most of the three years that Ruiu has been wrestling with badBIOS, its infection mechanism remained a mystery. A month or two ago, after buying a new computer, he noticed that it was almost immediately infected as soon as he plugged one of his USB drives into it. He soon theorized that infected computers have the ability to contaminate USB devices and vice versa.
• • •
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 laptop that had no obvious network connection with—but was in close proximity to—another badBIOS-infected computer. The packets were transmitted even when the laptop had its Wi-Fi and Bluetooth cards removed. Ruiu also disconnected the machine's power cord so it ran only on battery to rule out the possibility that 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 the internal speaker and microphone connected to the airgapped machine, the packets suddenly stopped.