.MSU File Extension

Update file used by Windows Update, an application included with Windows Vista, Windows 7, and Windows Server; contains updates for applications and files; installed by the Windows Update Stand-alone Installer (Wusa.exe), which is run by Windows Update automatically (the user generally does not need to manually install MSU files).

Each MSU file contains four elements:

1. Windows Update metadata, which describes the update package
2. One or more .CAB files that store the update data for the package
3. An .XML file which describes the contents of the MSU file
4. A properties file that is read by Wusa.exe

You can manually extract the contents of an MSU file at the Windows command prompt by typing:

expand -f:* "example.msu" output_directory

You can then manually install the update package by typing the following command:

pkgmgr.exe /n:output_directory\example.xml

(example.msu and example.xml have the same filename prefix).

NOTE: Earlier versions of the Windows operating system used .MSI files for updates.