What is a .msi file?

About the format

An .msi is a Windows Installer package — a database (in the old Compound File binary format, the same container as pre-2007 Office documents) describing what an installation should do: which files go where, which registry keys are written, which services are created, and how to undo all of it. Unlike a self-contained setup.exe, an .msi is executed by Windows' own msiexec service, which is why .msi installs integrate cleanly with Add/Remove Programs, support silent installation (msiexec /i package.msi /qn), per-machine vs per-user modes, repair, and rollback on failure — and why IT departments deploying via Group Policy or Intune prefer them. Double-clicking installs it; the same trust rules as .exe files apply, because an installer runs arbitrary custom actions. If you need to see inside one without installing, tools like Orca (Microsoft's table editor) or lessmsi list and extract the contents.

How to open a .msi file

Is a .msi file dangerous?

Same as any installer: it runs code with elevation. Source and signature are what count.

Related file types