FastSpy is Android surveillance malware used by Kimsuky and incorporated into later FastViewer variants. Operators distribute repackaged APK files that preserve the appearance and normal functionality of legitimate mobile applications while adding malicious code. Selected victims are induced to install these altered packages, giving the malware access through an application that appears familiar and functional. The merged FastViewer variant has been in production since at least July 2023 and places FastSpy within an evolving Kimsuky mobile toolset targeting Android devices through trojanized legitimate applications.