macOS High Sierra automatically checks a Mac's EFI firmware against Apple's database of "known good" data to ensure it hasn't been tampered with, according to a series of tweets from an Apple engineer.
The tweets have since been deleted, but a summary remains available on the Mac blog The Eclectic Light Company.
The new utility eficheck, located in /usr/libexec/firmwarecheckers/eficheck, runs automatically once a week. It checks that Mac's firmware against Apple's database of what is known to be good. If it passes, you will see nothing of this, but if there are discrepancies, you will be invited to send a report to Apple.If the check fails, a prompt will appear with options to "Send to Apple" or "Don't Send." The selection is remembered in subsequent weeks.
The "eficheck" tool sends the binary data from the EFI firmware, and preserves user privacy by excluding data which is stored in NVRAM, according to The Eclectic Light Company. Apple will then be able to analyze the data to determine whether it has been altered by malware or anything else.
The database's library will be automatically and silently updated so long as security updates are turned on.
EFI, which stands for Extensible Firmware Interface, bridges a Mac's hardware, firmware, and operating system together to enable it to go from power-on to booting macOS.
macOS High Sierra will be publicly released on the Mac App Store later today.