What are AAB files
AAB is an open-source format supported by mainstream build tools, including Android Studio, Gradle, Bazel, Buck, Cocos Creator, Unity, Unreal Engine, and others.

What are APK files
As we have seen, the acronym APK stands for Android Package, or Android package. APK files are compressed packages of app installation files for the Android operating system.

Most users are accustomed to seeing apps as downloadable programs from Google™ Play, without formats, files, folders and other technical and IT features. Yet when we install an app from Google™ Play, the platform uses exactly the same file types contained in an APK.

The APK format is used to compress these files into a single archive, which also reduces their size and makes them easier to transmit and manage.

Why install APK
Not all Android applications are on Google™ Play. Furthermore, some beta or even earlier versions of a certain program may no longer be available on the official Google™/Android platform.

In all these cases, we will have to search for the application APK, download and install it. There are various ways to do all this, but none of them use Google™ Play and this condition, as we will see shortly, can lead to security problems.

For Google™ and Android, an unknown origin is a web service from which to download data that has not been checked by the Google™ security network. Be warned though, not all unknown sources are dangerous, just as not all APK packages contain malware. In addition, sometimes even Google's security systems make detection errors or succumb to 0-day threats, and infected apps can also be found on Google™ Play.

That said, it remains an incontrovertible fact that apps from official stores such as Google™ Play are more secure than those installed via APKs. And it is equally true that most of the viruses for Android are spread via APK. For these reasons, if you want to download APKs and install them on your smartphone, we recommend that you:

Check the reliability of the site or source.
Install good cybersecurity software for Android, which protects you from viruses inadvertently downloaded to your phone.

Download APK
If you have decided to try to download an app or game in APK format, first of all we recommend that you do it only from the most well-known sites and suppliers. It is true that real gems can be found far from the official circuits and the most traveled roads, but it is also true that for each treasure there are thousands of infected applications, containing malware for Android.

Our advice is, at least at the beginning, to refer to the big names in the sector, such as AppsEnjoy.com

APK security
The fact that APKs are distributed outside of Google™ Play does not mean that there are no tools capable of verifying and certifying APK security, they are simply different from those used by Google™.

What are IPA files
An iOS application file is made with Apple's proprietary encoding specifications, and these encoding standards have been developed for the executable file format of programs developed for some Apple™ products.