Questions frequently come up about what to do in terms of Virus scanning virtual machines. Having virus scanning software installed and active on the host does not mean that the guests are immune to viruses. You should always install virus scanning on each guest as well - treat them as you would for any other physical machine. For performance reasons, on the host it is worth turning off exceptions for a number of file types: VHD, VUD, VSV, VFD, VMC - Hard Disks, Undo Disks, Saved States, Floppy Disks and Configuration files in order. Optionally, you may wish to turn off the ISO exception for virtual CDs/DVDs. Also on the host, you may choose to add vssrvc.exe (Virtual Server Service) as an exception.