How does Windows AppLocker work?

Windows AppLocker is a collection of Group Policy features you can use to control which applications are allowed to run on a system.

First introduced with Windows 7, AppLocker was created as a replacement for Windows' ineffective Software Restriction Policies  -- which still exist, even in Windows 10.

The Windows AppLocker settings exist within the Group Policy Object Editor at Computer Configuration > Windows Settings > Security Settings > Application Control Policies > AppLocker.

AppLocker is based on a series of rules that either allow an application to run or prevent it from running. There are four main types of AppLocker rules, and rules can be applied on a per-user or per-group basis. The rule types include Executable Rules, Windows Installer Rules, Script Rules and Packaged App Rules. These rules use application attributes as a mechanism to identify applications. For example, Executable Rules and Windows Installer Rules can identify an application based on its publisher, path or file hash.

AppLocker works, but it is far from perfect. It is a good tool for blocking specific applications. For example, if you want to phase out an application, you could create an AppLocker rule to prevent workers from using it. If on the other hand, your goal is to allow only certain applications to run, then you are probably be better off using a third-party tool. It is difficult to create a comprehensive set of rules for AppLocker, and something as simple as a software patch can render certain types of rules ineffective. As such, AppLocker is best suited for small jobs rather than comprehensive application protection.