Hyper-V Program Manager
Occasionally we hear reports of customer seeing bad interactions between Virtual PC / Virtual Server and antivirus programs on their host operating system. This seems to happen because Virtual PC / Virtual Server are making large amounts of changes to very large files - and this is not a typical file access pattern that Antivirus programs are expecting.
Problems that people usually see are random errors opening .VHD files and degraded performance of virtual machines.
To address this we recommend that users check their antivirus program to see if it can exclude .VHD, .VUD and .VSV files from live virus scanning. Doing this usually solves any problems - and does not increase the users risk to viruses as the host based virus scanner would not be able to detect a virus in the virtual machines by scanning these files anyway.