Introduction to Threats and Mitigations. Welcome to the fourth module of Secure Software Design specialization. We've already covered software design as an element of a life cycle, software design as an obstruction. We just finished too a course and design methods tools. In this course, we'll look at threats and mitigations. The basic outline of the course is to begin by looking at some open sources of information on threats and mitigations. We'll talk a bit about the appropriateness of biological analogies to security threats, viruses, worms, and so on. We'll look more carefully at the notion that secure design is just good design. We'll discuss why security is not an add-on, but rather a build-on. We'll discuss active verses passive security. And we'll finish with case studies on medical treatment devices, implanted medical medical devices and, finally, Bitcoin. Since this is the last module in specialization, we'll have a section on conclusions to wrap up secure software design. I think that the bottom line to this module would be that the threat is constantly changing and so the defenses must evolve too, thanks.