About msiexec.exe

msiexec.exe is a system process and part of Windows Installer. It is used to install Windows Installer packages (MSI) and is essential for the proper functioning of the system. It is often used when running Microsoft Update to install updates or to install certain software, and it can use a significant amount of memory.

Dependent service: Windows Installer
If you do not want it to load at system startup, you can disable the Windows Installer service.
To do so, open the Services app in the Control Panel > Administrative Tools, find the service named "Windows Installer," and set its properties to "Disabled."
If you need to use this process, simply set the properties back to "Automatic."

Recovery from Accidental Deletion

If you accidentally delete msiexec.exe, don't panic. You just need to use the repair function on the installation CD. Msiexec.exe is a component of Windows Installer. When Msiexec.exe is called by an installation program, it reads the package files (.msi), applies transform files (.mst), and merges the command-line options provided by the installation program. Windows Installer performs all installation-related tasks, including copying files to the hard drive, modifying the registry, creating desktop shortcuts, and displaying dialog boxes to prompt users for installation preferences if necessary.

When Windows Installer is installed on a computer, it changes the registered file type of .msi files so that double-clicking on an .msi file will run it together with Msiexec.exe.