VMware has released this week a new toolkit for virtual disk management that is looking very promising.

The VDDK provides easy access to virtual disk storage. This enables a wide range of solutions including:

Creation of virtual machine disk files to store backup of physical images. Read access to virtual disk to enable off-line centralized scanning of virtual machines for anti-virus. Write access to virtual disk to enable off-line centralized patching of virtual machines. Read access to virtual disk to enable off-line software package analysis of virtual machines.

The new API supports managing two kinds of disks; Managed Disks (local virtual diskfiles) and Hosted Disk (virtual disk files on you ESX/VMFS systems). This means the API will allow you to access disks remotely and opens a low of new opportunities for companies making virus scanning software, backup, forensic, etc.

More on the new API:
The Virtual Disk API Programming guide
The Virtual Disk Development Kit Homepage