Hardening, when applied to computing, is the practice of reducing a system’s vulnerability by reducing its attack surface.
Hardening may involve a reduction in attack vectors by culling the pathways, or vectors, attackers would use. Reducing these attack vectors involves system owners cutting unnecessary services or processes, and resetting default usernames and passwords.
Overall, a system that provides more services has a much broader attack surface than one performing just one function.
“Hardening our systems to make them more resistant to attack will entail discontinuing unneeded or unused services, as these entry points needlessly provide attack vectors through which cyberattacks are deployed. The fewer doors — the fewer unwanted visitors.”