What is the $hf_mig$
directory for in Windows Server 2003, and can I delete it?
2 Answers
Its name means "hotfix migration". It's for tracking versioning information about hotfixes to keep from accidentally breaking or downgrading your system. No, you definitely should not delete it.
Here's a good explanation of the topic: What is the “$hf_mig$” Folder for And Can I Delete It?