The file extension MSU is associated with Windows Vista Update Package, which is an installer for performing security updates to the Vista operating system. MSU files are included in Windows Vista and are installed using the Windows Update Stand-alone Installer.
The Stand-alone Installer is available for Vista, in addition to Windows 7 and Windows Server 2008. The installer is identified by a Wusa.exe file which is located in the System32 folder in the Windows directory. The Update Stand-alone installer relies on the Update Agent API to install updates to the Vista operating system. Each update package contains an MSU file extension.
MSU files contain metadata which describes the contents of the update package and a CAB file which represents the update. There is also an XML file which the Wusa.exe file uses to perform updates when you are away from your computer. Wusa.exe uses the metadata in the MSU file to continually search for appropriate Vista updates.
MSU files are a proprietary file and are typically in a compressed format which contains the files described above in a large archive format. The compressed format is used to save disk space since Windows continually releases operating system updates on a frequent basis.
How to Open MSU Files
Since MSU files are proprietary to Windows, you must use applications specifically designed for opened MSU file types. There are multiple methods you can use to open and view the contents of such files.
First, MSU files are a compression file type, which means you can use compression utility programs. There are two applications which are designed to open MSU files. They include Grumpy Snowmen, which is designed to open MSU files related to games, and MSU Motion Estimation Filter. Universal extractor is also a popular compression utility program which opens MSU files and is available as a free download on the Softpedia website.
You can also opt to use Vista Hotfix Installer Package, which is available as a free download from the Microsoft download website, or Blaise File, which is an open source program available for download on the Blaise website. Microsoft Update Stand-alone Installer will also help you open MSU files.
It is important to mention that MSU files are known to become corrupt, which causes difficulties with the Windows Update application. In this case, you can use a file repair software program such as FileCure to repair the MSU file. You can also choose to uninstall the file and then download it again manually from the Windows Update website.