[1] To run applications on the simulator, original project files which can be opened using the Xcode SDK are required.
A form of digital rights management exists in the format to control redistribution to a single Apple ID.
[2] Prior to iTunes 12.7 (September 2017), users had direct access to ipa files in the form of App Store downloads.
AltStore and Sideloadly are tools that can also be used to install unsigned .ipa files to unjailbroken devices by using a developer account to temporarily sign the app for 7 days for testing purposes.
Similar to the case of game console hacking, people are known to use this installation for piracy, against the tool developer's wishes:[7] some underground communities form around buying an app and then sharing its DRM-free unsigned version.