Describe the concept of security patterns and provide an example relevant to network security design.

• A. Security patterns are decorative motifs on user interfaces; example: color schemes.
• B. Security patterns are only for software design; not applicable to network.
• C. Security patterns are ad hoc fixes; example: patching after incidents.
• D. Security patterns are reusable solutions to common security problems; example: perimeter defense with multi-layered firewalling and intrusion detection.

Answer: (C)