Thanks for your replies. I have contacted Microsoft today, and I am allowed to run Windows 8.1 within the VM. That is, Kubuntu as host running VM, and install Windows 8.1 as the client. This is a single use of the product, it is not used anywhere else.  :)
Purchased a Dell laptop over a year ago. It came with Windows 8.1, but as I use Linux/Kubuntu, I wiped the disk and did a fresh install of Kubuntu. Later on, I purchased, from Dell, the Windows 8.1 , and my understanding is that this OS is OEM. Now I need to use Windows for data logs. Am contemplating using Oracle VM Virtual Box (  see [URL] ). Then Windows 8.1 can run from with the VM, with Kubuntu as the host. Can I legally use the Windows 8.1 in a VM environment ?  
Can I use Windows 8.1 in a VM environment ?