iOS or iPhone Operating System is the platform used to develop software, used in all Apple products . This includes iPhone, iPad and iWatch.
Typically all iOS apps will require review and approval by Apple, prior to release to the App Store. Therefore it is important that the code is written within the apple development guidelines. Given this process, iOS is typically designed with a well protected shell, that is almost impossible for virus to infect the app.
Apple typically releases a major update for IOS once a year, and therefore it is important to ensure that the apps are updated, so that the app still works seamlessly and has no bugs caused by the update.
THINGS TO CONSIDER WHEN DEVELOPING AN APP:
Choosing the target platform – iOS / Android or both.