Security is the degree of resistance to, or protection from, harm. It applies to any vulnerable and valuable asset, such as a person, dwelling, community, nation, or organization.
As noted by the Institute for Security and Open Methodologies (ISECOM) in the OSSTMM 3, security provides "a form of protection where a separation is created between the assets and the threat." These separations are generically called "controls," and sometimes include changes to the asset or the threat.
Perceived security compared to real security
Perception of security may be poorly mapped to measureable objective security. For example, the fear of earthquakes has been reported to be more common than the fear of slipping on the bathroom floor although the latter kills many more people than the former. Similarly, the perceived effectiveness of security measures is sometimes different from the actual security provided by those measures. The presence of security protections may even be taken for security itself. For example, two computer security programs could be interfering with each other and even cancelling each other's effect, while the owner believes s/he is getting double the protection.
Security theater is a critical term for deployment of measures primarily aimed at raising subjective security without a genuine or commensurate concern for the effects of that measure on objective security. For example, some consider the screening of airline passengers based on static databases to have been Security Theater and Computer Assisted Passenger Prescreening System to have created a decrease in objective security.
Perception of security can increase objective security when it affects or deters malicious behavior, as with visual signs of security protections, such as video surveillance, alarm systems in a home, or an anti-theft system in a car such as a vehicle tracking system or warning sign. Since some intruders will decide not to attempt to break into such areas or vehicles, there can actually be less damage to windows in addition to protection of valuable objects inside. Without such advertisement, an intruder might, for example, approach a car, break the window, and then flee in response to an alarm being triggered. Either way, perhaps the car itself and the objects inside aren't stolen, but with perceived security even the windows of the car have a lower chance of being damaged.