Ok, so you have a perfectly working Hyper-V environment…( Well, perfect is a strong word…) anyway, this is something that could be a problem, or a security risk or just a big mess.
Lets go back and take a look on a Hyper-V machine and its Network configuration, Every Hyper-V guru always point out the importance of having one dedicated management NIC and at least one NIC for all the VM’s and hi is 100% right, you should. Also You should disable the VM bus adapter that is created since the parent partition normally do not need access on that same network adapter, it has already access trough the management network adapter. This is perfectly fine, we all do this. (or should do) That means that if we look at a Hyper-V host it should look like this:
So, what’s the problem, well it is kind of easy. When installing SP2 for Windows Server 2008 the disabled network adapter will be enabled. Lets think here, what if that adapter is connected to a network outside, lets say the “Internet”, and for some strange reason there is DHCP out there. Then your Hyper-V server will directly connected to the Internet… scary. Or lets assume that this server is a part of a cluster, suddenly the cluster picks up a new network adapter. That does not mean that you will have a problem, but you are getting close. I have not tested this on core server but it should be the same effect, and that is even more scary, since that does not show up in the same way…
So, after you have installed SP2 for Windows Server 2008, make sure that your previous disabled network adapter remains disabled.