Microsoft is in the process of altering its servicing strategy for Windows as part of the Windows 10 Technical Preview to, hopefully, improve on a process that has had troubles in the past. If you are running Hyper-V hosts on Windows Technical Preview, you get to experience one of the first implementations of the evolving servicing strategy this afternoon.
Today, as part of the regular Patch Tuesday release, Hyper-V integration services will deliver directly to Windows Server 2008, Windows Server 2012 R2, Windows 7, and Windows 8 VMs running on Windows Technical Preview hosts, as long as the virtual machines are connected to Windows Update or a WSUS server.
The update delivering today in this manner is KB3004908, so you can watch for it.
In the past, upgrading a Hyper-V host took a lot of effort, caused downtime and reboots, and also required that the individual upgrading the host be given administrative rights. Updating in the new fashion ensures that virtual machines are updated consistently and automatically.