Non-jailbroken iOS devices can only install applications from the official Apple iTunes App Store. The App Store has an application approval process whose methods are not publicly disclosed, but that does not appear to do meaningful security checking of applications. Instead applications are checked for the use of undocumented APIs or other violations. Apple can disable installed applications via updating a blacklist that the device periodically checks.
- Apple’s App Store Submission Tips
- Gizmodo article on Apple’s ability to remotely disable applications
Applications for Android phones are typically installed via the Google Marketplace. Application APK files can also be copied onto the device and installed manually in a process called sideloading.
- Bright Hub’s How To Install and Remove Applications on Google Android Phones
- Bright Hub’s How to Install APK Files on Your Google Android Phone