the.com/hardening
Locking every door, not because you're paranoid, but because everyone outside actually is.
means The process of making a system, surface, or material more resistant to attack, failure, or deformation.
from From Old English 'heardian,' to make hard; the security sense borrowed the metaphor in the 20th century, treating software like fortified steel.
Security defaultDisable everything, then enable only what's needed.
Metallurgy twinHeat then quench steel to harden it.
Attack surfaceEach open port is another unlocked window.