Physical security: access control vestibules, badge readers, video surveillance, alarm systems, locks, guards, bollards, fences

Physical security protects people, buildings and equipment from unauthorized physical access. It matters to IT because anyone who can touch a computer or server can steal it, plug in a malicious device, or boot it from their own media and bypass many software controls. Strong passwords and encryption help, but they are much weaker when an intruder can carry the server out of the building. Good physical security uses several layers, so an intruder must defeat one barrier after another. This idea is called defense in depth.