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Windows file ID

1.  In the windows folder there exist three AU_X (where X is Backup, Log, and Temp) subfolders. Are these folders necessary? (temp is 30MB in size)
2.  There is the folder $hf_mig$ (139MB) What is it?  Is it necessary?
3.  There are about 45 folders named $NtUninstallKB...??...$ each about 3/4 MB  What are they? Are they necessary?
4.  There about 30 folders named $NtUninstallQ...??...$  What are they? Are they necessary
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3 Solutions
It may left when you install a particular software.

Try to disk cleanup the computer or use ccleaner to wipe unnecessary files.

The au_backup, au_log, etc. folders are from Trend-Micro Housecall antivirus.  See this page:

Removing Trend Micro Housecall remnants
temp folder files are usually unnecessary to boot.
Log files are for services like iis and smtp, they can go too.

$hf_mig$ is hotfix migration - I dont like deleting this, but I have in the past when desperate and it hasnt burnt me yet, ensure all your hotfixes have completed their patching first.

All the $NtUninstallKB...??... is for uninstalling knowledgebase patches, wont be able to reverse this if removed..

$NtUninstallQ...?  .. is similar to above.

Necessary for booting - no, to reverse changes - yes.

Per Microsoft: When a security update, critical update, update, update rollup, driver, or feature pack installs GDR (General Distribution Releases) 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: 1. 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. 2. 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.

so as you can see - in some situations it will be unrecoverable..

I am a little paranoid, so I moved them off disk first - a month later I deleted them...
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