Sorry for cross-posting, but this seems like the more appropriate sub-forum. Moderators, feel free to close my other thread I understand that running multiple hypervisors concurrrently can lead to problems. However, I have already determined it is safe to run VirtualBox VMs concurrently with Parallels Desktop 8 VMs, so long as I run: "VBoxManage modifyvm <VM name> --hwvirtexexcl off" to disable VBox's exclusive use of the hardware virtualization extensions. That, along with using VBox 4.2.12 (not the latest), enables me to run the two hypervisors side-by-side. I just upgraded to PD9 and I see that it actively detects when VirtualBox is running and forces any PD9 VMs to shut down. How can I override this to get back to the older PD8 behavior? I also want to note that VMware Fusion 5 runs concurrently with VirtualBox VMs; no workarounds needed, so it does seem possible. Thanks for any insight.