MED-V (Microsoft Enterprise Desktop Virtualisation) is their program that allows legacy app use on an enterprise wide basis and is based on Virtual PC technology.
It seems that some anti-virus programs have a habit of interfering with parts of the virtualisation if not properly configured. Steve Thomas, a Senior support escalation engineer at Microsoft, has drawn up a list of file extensions that should be masked to co-exist wth Anti-Virus on the network:
“*.VHD – These represent the Virtual Hard Disk Image files. These will appear on test workstations when test images are being used to finalize workspace policies.
*.VUD – These represent Virtual PC Undo Disk Files. These will appear on test workstations when test images are being used to finalize workspace policies.
*.VSV – These represent Virtual PC Saved State files. These will be on all MED-V clients running Workspaces.
*.CKM – This is the packed image format used by MED-V (Kidaro Compressed Machine.) These will be present on MED-V Servers, Image Distribution Servers, locally packed images on MED-V Administration workstations, and as pre-staged images on clients.
*.VMC – These represent the Base Virtual Machine Settings File. Will be found on all MED-V Clients and Test Workstations.
*.INDEX – These are index files used by the TrimTransfer Feature. These will be found on both clients and servers.
*.EVHD – These are the encrypted virtual hard disk files used on MED-V Clients running workspaces.”
Info from SoftPedia.
Cloudy with a chance of Licensing 
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