Microsoft unveiled this new feature at the Microsoft BUILD conference, being held this week in Anaheim, California. It will be available in Microsoft's Hyper-V version 3 hypervisor, included in Microsoft's next server operating system, Windows Server 8.

The capability, while viable in only a handful of use cases, nonetheless shows Microsoft's growing expertise in virtualization, analysts said.

With live migration, a working VM is moved from one computer to another without any disruption of the services offered by applications within the VM.

Most server virtualization software providers, including Microsoft, have long offered live migration within a local network. A far harder problem has been to offer the ability to move a live VM across different subnets, or separate WAN sub-networks. Network latencies and network addressing complexities have made this task .

At the BUILD conference, Microsoft program manager Ross Ortega explained how the new technology worked. Essentially, each virtual machine gets two IP (Internet Protocol) addresses.