[MUSIC] So, one of the important things to understand when building Android applications is how do I secure Android applications. We've all seen stories in the news about Apps that didn't properly secure their users data. And allowed other apps to read and write their private messages or contacts. And so, what this series of lectures is going to cover is what are sort of the basic things that you need to understand about how Android security works. And then, based on your understanding of what Android provides you from a security perspective. How you can write your app to improve its security? So, one of the first things to understand when we're talking about Android security, is how Androids version or how application or apps operates is different from what we see on a traditional desktop computing environment. So, in a traditional desktop and computing environment, if we launch an application, let's say it's a photo editor and we'll say this is our first app that we're launching. So, this is app one and let's say that that photo editor goes and we open it, and we decide that we want to access the internet maybe to download some images that we have stored on Facebook or Flickr. And then after getting those images. We go and we edit the images. And we save them to the storage on the disk. Now, one of the important things about the way that desktop environments work, is that they associate each app. That you launch with a single person, that is your user account. If you launch an app, that app is associated with your user account, and has all of the permissions and capabilities that are part of whatever's in your user account. So, this app will be part of your user account. And when you go and launch a second application, this is where this concept of each app running within your user account becomes important. So, if we go and we launch a second application, let's say that this is your browser and you're going to view in web browser, exactly what that image looks like. So, we will launch our web browser. This is our second application. One of the important things is this will also be running in our user account, and what that means is this application can go and directly access those same areas of storage that the first app could access. And the reason is that the privileges and permissions that are governing the web browser, which is another app that I, the user, have launched, are exactly the same, as the privileges and permissions of the first app. And that's because, I as a user launched both of these applications and therefore both of them are associated with my user account.