Along with new features in Android 4.2, there is significant enhancements in the security system. The Android 4.2 security system is integrated into the mobile OS, and is always on the lookout for problems. The key component is a real-time app scanning service that instantly checks apps put on your device for any malicious or potentially harmful code. This feature is an extension of the Google Play Store’s security technology, which analysis apps uploaded to the store for maliciousness. While that technology worked exclusively on the server side, analysing apps that were uploaded to the Play Store, the new system works with your device and scans any apps you install from third-party sources (a process known as "sideloading"). This offers users protection from malicious apps that aren't vetted by the Play Store’s security system.
Also included in the new security suite of services for Android 4.2, is a system that will warn you if a text messaging service is trying to send out messages that could cost you money. If your phone discovers one of these, it will stop the service and then let you decide if you want to allow the action to happen or not.
Last, the app permissions page that pops up during app installs has been refined. The new Android 4.2-level screen is cleaned up and far easier to read than what we've seen in the past.