With all the news regarding the Spectre and Meltdown CPU vulnerabilities over the past several months, there’s been a greater focus to get VMware virtual machines to virtual hardware version 9 or higher, as noted by Andrea Mauro’s post regarding these vulnerabilities. In addition to that, several companies and organizations may be looking to enable Secure Boot, a feature first introduced with vSphere 6.5. However, in order to enable secure boot, the virtual machine needs to be configured with both EFI boot firmware AND be on virtual hardware version 13 or higher.
Doug's Blog 