Android: unable to uninstall application

Problem:
A friend of mine wanted to uninstall an app from his Android phone. But for some reasons, the "Uninstall" option is disabled. I tried running adb uninstall <package_name>, but it failed to uninstall.

Checking logcat, there was a warning:
W/PackageManager: Not removing package com.foo.bar: has active device admin


Solution:
Basically, this app has device admin features enabled, meaning it can erase your phone's data if you lost your phone for example. So we need to first go into Settings > Location and Security > Device Administrator, and disable the app before we can uninstall it.


Ref:
uninstall - How to remove an app with active device admin enabled on Android? - Stack Overflow