If you have the “Show hidden files and folders” option enabled, you may have noticed a folder named “$hf_mig$” inside of your Windows directory. This folder contains information about previously installed updates. According to Microsoft, “When a security update, critical update, update, update rollup, driver, or feature pack installs GDR version files, the hotfix files are also copied to the %windir%\$hf_mig$ folder. This supports migration to the appropriate files if you later install a hotfix or service pack that includes earlier versions of these files.”
For example, consider the following scenario:
- You apply a security update that installs a GDR version of File.dll with a version number of 5.2.3790.1000 and copies a hotfix version of File.dll with a version number of 5.2.3790.1000 to the %windir%\$hf_mig$ folder.
- You apply a hotfix that includes a hotfix version of File.dll with a version number of 5.2.3790.0000.
In this scenario the hotfix installation in step 2 installs the hotfix version of File.dll (version number 5.2.3790.1000) from the %windir%\$hf_mig$ folder instead of the hotfix version of File.dll (version number 5.2.3790.0000) from the hotfix package.
Because the “$hf_mig$” folder is crucial to ensuring your computer has the most recent updates, you SHOULD NOT delete the “$hf_mig$” folder.