The ultimate guide to Windows 7 security

Microsoft's most sophisticated solution to the problem is AppLocker, an application-control feature included in Windows 7 (Ultimate and Enterprise editions) and Windows Server 2008 R2. AppLocker is an improvement on the Software Restriction Policies (SRP) introduced with Windows XP Professional. AppLocker allows you to define application execution rules and exceptions based on file attributes such as path, publisher, product name, file name, file version, and so on. You can then assign policies to computers, users, security groups, and organizational units via Active Directory.

Configuring AppLocker. You can configure AppLocker locally using the Local Computer Policy object (gpedit.msc) or via Active Directory and Group Policy Objects (GPOs). AppLocker relies on the built-in Application Identity service, which is normally set to manual startup type by default. Administrators should configure the service to start automatically.

Within the local or group policy object, AppLocker is enabled and configured under the \Computer Configuration\Windows Settings\Security Settings\Application Control Policies container.

By default, AppLocker rules do not allow users to open or run any files that are not specifically permitted. First-time testers will benefit by allowing AppLocker to create a default set of "safe rules" using the Create Default Rules option. The default rules authorize all files in Windows and Program Files to run, along with letting members of the Administrators group run anything.

One of the most notable improvements over SRP is the ability to run AppLocker against any computer using the Automatically Generate Rules option to quickly create a baseline set of rules. In a few minutes, dozens to hundreds of rules can be produced against a known clean image, saving administrators anywhere from hours to days of work.

Running by the rules. AppLocker supports four types of rule collections: Executable, DLL, Windows Installer, and Script. SRP administrators will notice that Microsoft no longer has the registry rules or Internet zones options. Each rule collection covers a limited set of file types. For example, executable rules cover 32- and 64-bit .EXEs and .COMs; all 16-bit applications can be blocked by preventing the ntdvm.exe process from executing. Script rules cover .VBS, .JS, .PS1, .CMD, and .BAT file types. The DLL rule collection covers .DLLs (including statically linked libraries) and OCXs.

If no AppLocker rules for a specific rule collection exist, all files that share the same format are permitted to run. However, once a rule for a specific collection is created, only the files explicitly allowed in the rule can execute. For example, if you create an executable rule that allows .EXE files in %SystemDrive%\FilePath to run, only executable files located in that path are permitted to run.