“Three years ago, security consultant Dragos Ruiu was in his lab when he noticed something highly unusual: his MacBook Air, on which he had just installed a fresh copy of OS X, spontaneously updated the firmware that helps it boot. Stranger still, when Ruiu then tried to boot the machine off a CD ROM, it refused. He also found that the machine could delete data and undo configuration changes with no prompting. He didn’t know it then, but that odd firmware update would become a high-stakes malware mystery that would consume most of his waking hours.”
Source: Meet “badBIOS,” the mysterious Mac and PC malware that jumps airgaps | Ars Technica