Security is the degree of resistance to, or protection from harm. Security can apply to anything of value, be it information, assets, people or entire nations.
The perception of security can be in itself a form of security. Places which seem difficult to penetrate will deter casual attempts. While casual attempts would be defeated by the security measures, it is more cost effective and efficient to deter the attempts in the first place.
The take away on this is that good security looks the part. Visible obstructions to entry, visible surveillance, visible alarms, visible counter measures. These may not be the entire security, they often aren’t, but highly visible components are essential to protecting an asset.
From a game perspective this is useful. It allows us to sell the scene to the players and set tension. Describe the alert guards, the sweep of security drones, the glint of micro wire fences. Comment on the suppression of node traffic as Black IC hovers over a users icon then passes on. Describe the searing color of astral wards, the hypnotic pulse and menace of spirits. Draw the players in by scaring them a bit.
All security systems have some common characteristics. There is the Asset, the Risks/Threats to the Asset, Countermeasures to the Risks/Threats, and Vulnerabilities to the Countermeasures.
Put in a different format, security protects an asset from risks and threats. The way it does so is a countermeasure of some sort. Unfortunately nearly every countermeasure has some way to be defeated or avoided, this is a vulnerability.
Security seeks to deter Threats via the above perception of security. Scary guards and alarms prevent initial attempts. Once a threat moves into the sphere of security and the asset it encounters a countermeasure. Countermeasures can be passive, as with the appearance of security, reactive in the case of alarms, or active, as would be the case for sentries or guards.
In Shadowrun there are three main arenas to worry about. Physical, Matrix, Astral. Physical security is something most people are aware of in passing. Guards at doors, metal detectors, alarms, walls fences ditches. All countermeasures to a physical threat. They do mostly dick all to a non physical threat. This is generally true across the three arenas. An Astral Countermeasure rarely interacts with a Physical threat and vice versa.
Learning what are common security countermeasures in each arena is important to running a challenging and immersive game of Shadowrun. You don’t need to know every single stat, but you do need to have an idea of how security works so that you can present a comprehensive challenge to players.