Several malware applications can trick the Android users to install these and after the installation was performed, these have the ability to avoid being uninstalled from devices.
Also, most malicious apps can exploit some vulnerabilities to run itself with hidden device administrator rights. In most situations your Android OS can't detect and uninstall these malware apps, but major security software vendors designed other apps that can offer you the opportunity to remove the device admin rights of these apps in order to be uninstalled.
Hidden Device Admin Detector is a free scanning tool that helps you to check your Android device against malware apps that are installed into your gadget with device administrator privileges (in most times these apps are hidden from the view list of your installed applications).