MSU File Extension

What is MSU file?

MSU is an update installer file format used by Windows Update application included in Windows Vista operating system. MSU file stores file and application updates (security updates, system updates, or patches).

MSU file contents

Each MSU file contains the following elements:

• Windows Update metadata – information that describe each update package in given MSU file;
• at least one CAB file – CAB files store the actual update data;
• XML file – contains information describing contents of MSU package;
• properties file – the file is read by Wusa.exe program that searches for appropriate updates and applies them automatically.

MSU format and data compression

MSU is a proprietary format. MSU files are typically compressed to save disk space as Windows update packages are released frequently and can be quite large.

Automatic update installation

Udates in MSU files are installed by Windows Update tool, which is run by Wusa.exe program located in System32 folder on Windows system. Installer uses Windows Update Agent API for applying updates. Contents of MSU files can be extracted manually and then installed using appropriate Windows command line instructions.

Programs which support MSU file extension

Programs that can handle MSU files are as follows. MSU files can be encountered on all system platforms, including mobile, yet there is no guarantee each will properly support such files.

Updated: 01/31/2022

How to open file with MSU extension?

Being unable to open files with MSU extension can be have various origins. Fortunately, most common problems with MSU files can be solved without in-depth IT knowledge, and most importantly, in a matter of minutes. The list below will guide you through the process of addressing the encountered problem.

Step 1. Download and install Microsoft Windows Update

Problems with opening and working with MSU files are most probably having to do with no proper software compatible with MSU files being present on your machine. This issue can be addressed by downloading and installing Microsoft Windows Update or different compatible program, such as Microsoft Windows 8, Microsoft Windows Vista, Microsoft Windows 7. On the top of the page a list that contains all programs grouped based on operating systems supported can be found. The safest method of downloading Microsoft Windows Update installed is by going to developer’s website () and downloading the software using provided links.

Step 2. Update Microsoft Windows Update to the latest version

If the problems with opening MSU files still occur even after installing Microsoft Windows Update, it is possible that you have an outdated version of the software. Check the developer’s website whether a newer version of Microsoft Windows Update is available. Software developers may implement support for more modern file formats in updated versions of their products. If you have an older version of Microsoft Windows Update installed, it may not support MSU format. The most recent version of Microsoft Windows Update is backward compatible and can handle file formats supported by older versions of the software.

Step 3. Set the default application to open MSU files to Microsoft Windows Update

If the issue has not been solved in the previous step, you should associate MSU files with latest version of Microsoft Windows Update you have installed on your device. The method is quite simple and varies little across operating systems.

Selecting the first-choice application in Windows

• Choose the Open with entry from the file menu accessed by right-mouse clicking on the MSU file
• Select Choose another app → More apps
• To finalize the process, select Look for another app on this PC entry and using the file explorer select the Microsoft Windows Update installation folder. Confirm by checking Always use this app to open MSU files box and clicking OK button.

Selecting the first-choice application in Mac OS

• Right-click the MSU file and select Information
• Open the Open with section by clicking its name
• Select the appropriate software and save your settings by clicking Change all
• A message window should appear informing that This change will be applied to all files with MSU extension. By clicking Continue you confirm your selection.

Step 4. Ensure that the MSU file is complete and free of errors

If you followed the instructions form the previous steps yet the issue is still not solved, you should verify the MSU file in question. Problems with opening the file may arise due to various reasons.

1. Check the MSU file for viruses or malware

If the MSU is indeed infected, it is possible that the malware is blocking it from opening. Scan the MSU file as well as your computer for malware or viruses. If the scanner detected that the MSU file is unsafe, proceed as instructed by the antivirus program to neutralize the threat.

2. Ensure the file with MSU extension is complete and error-free

If you obtained the problematic MSU file from a third party, ask them to supply you with another copy. During the copy process of the file errors may occurred rendering the file incomplete or corrupted. This could be the source of encountered problems with the file. It could happen the the download process of file with MSU extension was interrupted and the file data is defective. Download the file again from the same source.

3. Ensure that you have appropriate access rights

Some files require elevated access rights to open them. Log out of your current account and log in to an account with sufficient access privileges. Then open the Windows Vista Update Package file.

4. Check whether your system can handle Microsoft Windows Update

The operating systems may note enough free resources to run the application that support MSU files. Close all running programs and try opening the MSU file.

5. Check if you have the latest updates to the operating system and drivers

Up-to-date system and drivers not only makes your computer more secure, but also may solve problems with Windows Vista Update Package file. Outdated drivers or software may have caused the inability to use a peripheral device needed to handle MSU files.

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