Today, new information got released about Microsoft's plans for the Universal Windows Platform. Windows 10 will get a more secure encrypted appx format so no one will be able to modify these apps.
With these changes however, when the user installs an app from the Windows Store, it will get encrypted on-the-fly using the Encrypting File System feature of Windows.
Once encrypted, app files will not be accessible for modification even if full access permissions are granted.
Because of this change, Microsoft can finally offer protection to developers against apps getting decompiled and against piracy and easy app modification, which has always a problem for developers due to the .NET platform heritage. Now apps should become more secure and safe. (credits: WalkingCat).