Taylor Brown has been running a series of posts on his blog about Hyper-V Data Exchange. It’s one of the integration services available on each VM. The idea is that you can query a certain section of the registry (HKEY_LOCAL_MACHINESOFTWAREMicrosoftVirtual MachineGuestParameters) on either the guest or the parent. You can also write to there as well.
That brought up a question in my mind. There are some environments where this would be very bad. Can you disable this? Sure you can! Open up the properties of the VM in question and clear the tick box for the Data Exchange integration service. Voila: it’s disabled.