How should we back up virtual machines and hypervisors?
Back up the virtual machines with a tool that understands the hypervisor, so that you can restore a whole machine quickly, and also protect the hypervisor layer itself. Many current ransomware families include versions built to encrypt VMware ESXi hosts directly, which takes down every virtual machine on them at once. Practical points: keep the hypervisor management interfaces off the general network and reachable only from admin workstations; use separate, MFA-protected accounts for hypervisor and backup administration; disable services you do not need, such as SSH on hosts outside maintenance; patch hypervisors promptly; and make sure at least one backup copy sits outside the virtual environment it protects, immutable or offline. Hypervisor snapshots are useful for quick rollbacks but are not backups: they live on the same storage and disappear with it. Test restoring a full virtual machine to different hardware, because after an attack the original host may be unavailable.