You going for the CIA description of information security:

Confidentiality, Integrity and Availability.

When you look at hardware security in terms of the CIA then reliablility becomes important in terms of integrity and availability and are easily measurable for hardware. Computer broke = no availability = security failure.

Hard drive corrupts = loss of data integrity = security failure
Network card losing packets = loss of integrity and availability.
Poorly designed CPU allowing overflows could = failure in confidentiality if the intruder gets root.


Think of an issue and think about how it affects CIA of a system.