When you visit Windows Update to download and install an update, you receive:
The software you are about to install does not contain a Microsoft digital signature. Therefore, there is no guarantee that this software works correctly with Windows.
Unknown software package.
If you respond Yes, the installation continues.
Microsoft does NOT post unsigned packages to the Windows Update site, but some of the files in the package may be unsigned.
If you configured the Unisigned non-driver installation behavior to Warn but allow installation, you will receive the above message when a package contains an unsigned file. This policy is configured in the Default Domain Group Policy at Computer Configuration / Windows Settings / Security Settings / Local Policies / Security Options or in the Local Security Policy at Security Settings / Local Policies / Security Options.
If you have set this policy to Warn but allow installation, simply verify that you are downloading from Windows Update and press Yes to proceed with the installation.