Windows Update Agent (WUA) automatically updates itself when it is connected to a Windows Server Update Services (WSUS) server or to Windows Update. WUA can also be updated by using a signed installation package that is available from Microsoft. The installation package can be used to install the latest released versions of WUA or of the Muauth.cab file.

Follow these steps to obtain the installation package for the latest version of WUA.

To obtain the installation package for the latest version of WUA

1. Download the Wuredist.cab signed cabinet file.

   Note  This file contains information about the installation package for the latest version of WUA. You can download this file from http://update.microsoft.com/redist/wuredist.cab.

2. Verify that the Wuredist.cab file has a digital signature from Microsoft. If you update WUA manually, right-click Wuredist.cab, click Properties, and then click the Digital Signatures tab.

   Verify that Microsoft Corporation appears in the list of digital signatures. Applications should verify the digital signature by using the application programming interface (API) that is described in the security section of the Microsoft Platform Software Development Kit (PSDK).

3. Extract the XML file from the Wuredist.cab file. The Microsoft Cabinet SDK contains information and tools that you can use to extract files from a cabinet.

   The XML file contains a <StandaloneRedist> element, as shown in the following example. This information identifies the most recent WUA version and gives the URLs for the locations of the installation package downloads.

   <?xml version="1.0" ?> 
   <StandaloneRedist Version="20">
     <architecture= "x86" clientVersion="5.8.0.2339" downloadUrl="http://download.windowsupdate.com/v6/windowsupdate/redist/standalone/WindowsUpdateAgent20-x86.exe"/>
     <architecture= "x64" clientVersion="5.8.0.2339" downloadUrl="http://download.windowsupdate.com/v6/windowsupdate/redist/standalone/WindowsUpdateAgent20-x64.exe"/>
   
     <MUAuthCabRevisionId= "5" downloadUrl="http://download.windowsupdate.com/v6/windowsupdate/redist/standalone/MUAuth.cab"/>
   </StandaloneRedist>

   The fields in the <StandaloneRedist> element have the following meanings:

   • The Version attribute is the major version of the WUA installation package.

     Currently, the only available version is version 20.

   • The architecture attribute specifies whether the installation package is for computers that are running a 32-bit version of Windows or a 64-bit version of Windows.

     Users need to identify and download the correct installation package for their computers. The possible values for this attribute are x86 or x64.

   • The clientVersion attribute specifies the full version of WUA that is installed by the installation package.

     Compare this to the version that is returned by the IWindowsUpdateAgentInfo::GetInfo method to determine whether the package installs a later version of WUA. For example, version 5.8.0.2339 is later than version 5.8.0.2330.

   • The downloadUrl attribute specifies the URL for the download and the installation of the Windows Update package.
   • The MUAuthCabRevisionId attribute specifies the revision number of the Muauth.cab file that the package downloads and installs.
4. Compare the version of WUA that is currently running on the client computer to the version that is available in the installation package. For more information about how to determine the version of WUA that is running on the client computer, see Determining the Current Version of WUA.

   Use the IWindowsUpdateAgentInfo::GetInfo method or check the version of Wuaueng.dll that is currently running in the \System32 subdirectory of the current Windows installation.

5. Update the WUA API header files. For more information, see Updating Windows Update Agent Header Files.

Consider the following example. A user or application that is running on a 32-bit Windows-based computer may determine that the current version of WUA on the computer is 5.8.0.2330. After downloading Wuredist.cab and extracting the XML file, the user or application finds that the file contains the following XML:

<architecture= "x86" clientVersion="5.8.0.2339" downloadUrl="http://download.windowsupdate.com/v6/windowsupdate/redist/standalone/WindowsUpdateAgent20-x86.exe"/>

Because version 5.8.0.2339 is a later version than version 5.8.0.2330, a later version of WUA for x86-based computers is available in the installation package. In this example, a later version of WUA can be downloaded to and installed on the computer from the URL that is specified by the value of downloadUrl: http://download.windowsupdate.com/v6/windowsupdate/redist/standalone/WindowsUpdateAgent20-x86.exe.

If the version of WUA in the package is earlier than the version that is currently running on the computer, installing the package does not replace the later version.

Send comments about this topic to Microsoft

Build date: 5/15/2008