Secure by design, in software engineering, means that the software has been designed from the foundation to be secure. In such approach, the alternate security tactics and patterns are first thought; among them, the best are selected and enforced by the architecture design, and then used as guiding principles for developers. Secure by Design is more increasingly becoming the mainstream development approach to ensure security and privacy of software systems. In this approach, security is built in the system from the ground up and starts with a robust architecture design. Security architectural design decisions are often based on well-known security tactics, and patterns defined as reusable techniques for achieving specific quality concerns. Security tactics/patterns provide solutions for enforcing the necessary authentication, authorization, confidentiality, data integrity, privacy, accountability, availability, safety and non-repudiation requirements, even when the system is under attack. In order to ensure the security of a software system, not only it is important to design a robust security architecture (intended) but also it is necessary to preserve the (implemented) architecture during software evolution. Malicious practices are taken for granted and care is taken to minimize impact in anticipation of security vulnerabilities, when a security vulnerability is discovered or on invalid user input. Closely related is the practice of using "good" software design, such as domain-driven design or cloud native, as a way to increase security by reducing risk of vulnerability-opening mistakes—even though the design principles used were not originally conceived for security purposes.