> Our guess is that this unknown hardware feature was most likely intended to be used for debugging or testing purposes by Apple engineers or the factory, or that it was included by mistake. Because this feature is not used by the firmware, we have no idea how attackers would know how to use it.
However, keep in mind that this level of "bugdooring" is possible without Apple's explicit cooperation. In fact, the attackers don't even need to force a bug into the code. It would probably be sufficient to have someone on staff who is familiar with the Apple hardware development process (and therefore knows about the availability of these tools), or to simply get a copy of the firmware's source code. Sophisticated attackers likely have moles embedded within Apple. But they don't even need that here; they could just hire an ex-Apple employee and get all the intel they need.