Oct. 2020 article about Chinese rootkit exploit refers to it as "invisible enemy".

"Fighting the Invisible Enemy

It's not easy to even track these types of attacks because there's little visibility into them, researchers say. So, how do you protect against a bootkit attack?"

https://www.darkreading.com/threat-intelligence/rare-firmware-rootkit-discovered-targeting-diplomats-ngos-/d/d-id/1339110