A key update viewed in many eyes for any Hyper-V environment.
Released back in April 2015, a new security vulnerability has been discovered which could result in a denial of service to a virtual machine running in Hyper-V. Even thou this may not impact other running virtual machines this could affect manageability of the underlying hosts.
The following Microsoft KB provides further info and patch information. https://support.microsoft.com/en-us/kb/3047234
As per best practice, it best to ensure your Hyper-V environment’s have been fully patched with all the latest hot fixes and patches. The following articles should be used as guidance on what to install.