We're going to talk about sustainability in the context of security now. For any app or other application to be successful, it's going to have go and live through a whole bunch of different versions. It's going to have all kinds of outside external influences on that app. It's going to interact with users. It's going to interact with other systems. New things are going to emerge. It's constantly going to be facing different pressures from the outside. And one of the pressures that it's going to always face is security and attacks. So we will always want to make sure that we are prepared to handle this aspect of our app sustainability and evolution of over time. The security of our app. Now, why is security so tightly interwoven with sustainability? Well, unfortunately, we don't live in a world where nothing bad ever happens. Unfortunately cyber attacks are reality, and we have to make sure that, when we're designing software, we try to think about our users and really care about our users. Because when we build software for other people, or other organizations, and we accidentally create security vulnerabilities in them, we are inevitably exposing them, and potentially their really personal information, or their really private operations, or intellectual property. Or we're potentially exposing some really important system, like a power grid. So we want to make sure that we really take that into account when we're designing our application, and make security an important aspect of our design and evolution. Now, another reason we want to do this is, if you want to just think selfishly about it, if your app, if some version of your app is shown to be insecure. So suddenly we see here, and there's some vulnerability that's discovered in your app. And it's discovered, it's widely known that it's highly vulnerable. Your users are going to flee from that version of that app. They're going to stop using it. And so, unless you can quickly fix and mitigate that vulnerability and take care of it, your app will not be sustainable. It will no longer be used. It will essentially die at that point in time. So another thing to think about is if a vulnerability is discovered, you've then impacted all these users. And the impact could be so damaging that then no one wants to use your app because of the risk of using it. Or, if a vulnerability is discovered and it takes you so long to go and fix that vulnerability that the users are really upset by it, they may not come back and use your app when you have fixed it. They may just abandon it altogether and switch to something else that does take security vulnerability seriously And make it so that they can evolve quickly to fix security vulnerabilities. So security and making sure your app is secure is absolutely a critical aspect of sustainability. If you can't go from one version to another without guaranteeing or trying to account for security, and when security problems are found, if you can't quickly fix them, your app is not going to be sustainable. People aren't going to use it. And you're also going to cause damage with your app if you're not thinking through the security aspects. So we really want to make security an important aspect of sustainability. And it's a critical part of software development.