TrustedInstaller on some Windows Vista systems can essentially hang for several minutes consuming 100% of the CPU cycles, which makes the computer unusable until the TrustedInstaller.exe process terminates itself. The purpose of TrustedInstaller is to act as the gatekeeper and protect essential system resources, such as files, folders, and registry keys, that are critical to keep Windows Vista stable. When a program installed on your computer tries to access system files, TrustedInstaller starts automatically to prevent the program from modifying critical system files. On startup TrustedInstaller can sometimes consume 100% of the system resources, or less, to do its job. Microsoft will most likely address this, and other issues in their first service pack for Vista which is expected soon.

For background and FYI purposes here is how TrustedInstaller is defined.

TrustedInstaller Windows Services definition:
Adds, modifies, and removes applications provided as a Windows Installer (*.msi) package. If this service is disabled, any services that explicitly depend on it will fail to start.

TrustedInstaller Other definition:
trustedinstaller.exe is a Windows Modules Installer from Microsoft Corporation belonging to Microsoft® Windows® Operating System. This enables management of Windows updates.

There are two ways to stop TrustedInstaller from causing problems by consuming all your system resources during startup.

1) Modify Service Setting

To quickly access the Services window use the shortcut keys Win+r. Win stands for Windows Logo Key. In the Run box type:

control services

… and hit enter.

The long way to access the Services window is to click the Windows Logo icon in the bottom left corner –> Control Panel –> System Maintenance –> Administrative Tools –> Services. Now scroll down until you see Windows Installer, and double-click it to open the dialog window.

On the General tab set the Startup type selection to Manual.

Click the Recovery tab, then change the First Failure selection from Restart the Service to Take No Action.

Now click OK. When you reboot your computer the TrustedInstaller should not start, but it will start when programs try to modify a critical system file, folder, or registry key.

2) Kill TrustedInstaller.exe on Startup

To eliminate altering the Service settings, I have written a script that will kill the TrustedInstaller.exe when your computer startsup. This should keep TrustedInstaller from consuming resources during startup, but still function properly when needed. First click the Windows Logo Icon –> All Programs, now right-click Startup, and select Open.

Click here to download the TrustedInstaller killer script, unzip it, and copy the file into the Startup folder. Now close the folder.

Each time the computer starts up you’ll see a black command window flash. That is the script killing the TrustedInstaller.exe process automatically.

To remove the script simply delete it from the Startup folder. You can also put the TrustedInstaller killer script on your desktop to kill the script manually with a double-click on the file.

Are you getting "Unable to save permission changes on file_name. Access is denied." error messages when trying to modify a file or change permissions on a file that has TrustedInstaller as its owner? It is possible to take ownership away from TrustedInstaller, and give it to your Administrative account, but it is not wise to mess with System Files. TrustedInstaller is a special service that manages “essential” resources (system files, folders, and registry keys) that are critical to the operation of Windows Vista. To prevent application and operating system failure, these resources are protected using Windows File Protection (WFP) in such a way that applications or users cannot modify these resources. The way this protection is implemented is by setting an ACL on these resources only to allow only the TrustedInstaller user to modify them. When setup applications try to modify a protected system resource it will not get an error as mentioned above, however Vista will detect the installation program, and the request will be accepted and a success code will be returned, but the resource will not be modified. This is why you may have the need to take permission of a system resource, so you can modify it manually.

If you gave ownership of a system resource to yourself, so you could modify the resource, and now you want to give ownership back to TrustedInstaller, simply follow these steps:

Right-click on the file and choose Properties
Click Security tab
Click Advanced button
Click Owner tab
Click Edit button
Click Other User or Group and type in:

NT SERVICE\TrustedInstaller

Press Ok on all dialogs until all property dialogs are closed

For instructions on how-to take ownership from TrustedInstaller, and give ownership to yourself to modify a file click here.