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I recently reformatted my external hard drive using NTFS. Everything seems to be working fine except for a mysterious folder that has appered in the root of my drive.

E:\>cd a4c065edd6b8178c4f4637f59d

 Volume in drive E is Miff
 Volume Serial Number is BA4D-9E70

 Directory of E:\a4c065edd6b8178c4f4637f59d

2009-10-26  04:57 PM    <DIR>          .
2009-10-26  04:57 PM    <DIR>          ..
2009-10-26  04:56 PM         1,326,464 1CD34F99-3C46-4C0B-B747-C3DD63D55C14mpavdlta.vdm
2009-10-26  04:56 PM           630,144 6B4511E8-3FB4-4D77-9AEE-C292202D7414mpasdlta.vdm
               2 File(s)      1,956,608 bytes
               2 Dir(s)  498,944,262,144 bytes free


What is the meaning of these files? Where do they come from? Can I delete them?

UPDATE: They seem to be spreading, now there's four of them, each one a hex string of the same legnth.

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up vote 3 down vote accepted

Those files are the delta definitions for MS Forefront. I'd assume Microsoft stores them temporarily in the root of the largest available partition.

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Would that include Microsoft Security Essentials? – MiffTheFox Oct 27 '09 at 11:30
It's very possible. Forefront is the paid version of their security, so I'd imagine they use the same definitions for both products. – MDMarra Oct 27 '09 at 13:52
Can they just be deleted with no ill effects? – Patriot Nov 3 '09 at 15:54
I believe so. Most AVs will use this temp space to handle the definition files during download, then they are typically imported into the AV software's permanent storage place for DATs. An easy way to check is to delete it and check Forefront or Security essentials and see what the version and date of the definitions are. If it is current and everything works fine then yes, if not restore them. Note: I do not use Forefront or MSE, so I'm just listing a generic way to check. – MDMarra Nov 3 '09 at 16:28
Renaming them seems to have no effect, so I deleted them. Also: there's more info here: – MiffTheFox Nov 13 '09 at 5:11

I have these too. It might be related to MS Security Essentials - seems it appeared after the last Essentials update.

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