Microsoft has a remedy for keeping offline virtual machines updated.
Virtual Machine Servicing Tool 2.0 lets IT managers send operating system updates to virtual machines that are stored in the System Center Virtual Machine library. The tool should prevent offline machines from spreading vulnerabilities once reconnected to the network, according to Microsoft.
The offline tool uses the Windows Workflow programming model and the PowerShell interface to create a temporary connection to offline virtual machines for updating from WSUS or Microsoft's System Center Configuration Manager 2007 desktop management tool.
Virtual Machine Servicing Tool 2.0 adds support for Hyper-V, VMM 2008 and Windows Server 2008, System Center Configuration Manager 2007 SP1 and R2 and WSUS 3.0 SP1.