Outhere is (certainly outdated ) a catalogue of NSA firmware-hacking tools (ARKSTREAM) for BIOS-spy hacking.
Proprietary BIOS firmwares (installed at manufacturing time) are many years now with malicious implants (payloads) which operates above antivirus and any available OS.
Over a billion machines running proprietary BIOS.
BIOS malwares uses certain functions with high-level system privileges to read all data and code that appears into a machine’s memory.
Even the Tails Linux, system that Snowden use to protect himself can’t actually protect him from the NSA or anyone else if use the proprietary UEFI firmware and BIOS.
Possible solution/replacement - LinuxBIOS (Coreboot, Libreboot and SageBIOS) is available only for a limited number of hardware platforms, on the approximately 200 supported motherboards in total.
The truth is sad and hard to swallow