As any nagging cybersecurity expert will tell you, keeping your software up to date is the brushing and flossing of digital security. But even the most meticulous practitioners of digital hygiene generally focus on maintaining the updates of their computer’s operating system and applications, not its firmware. That obscure, reptile-brain code controls everything from a PC’s webcam to its trackpad to how it finds the rest of its software as it boots up. Now one new study has found that the most critical elements of millions of Macs’ firmware aren’t getting updates. And that’s not because lazy users have neglected to install them, but because Apple’s firmware updates frequently fail without any notice to the user, or simply because Apple silently stopped offering those computers firmware updates—in some cases even against known hacking techniques.