Two teams of researchers managed to win the biggest bounties at this year's Pwn2Own hacking contest by escaping from the VMware Workstation virtual machine and executing code on the host operating system.
Virtual machines are in used in many scenarios to create throw-away environments that pose no threat to the main operating system in case of compromise. For example, many malware researchers execute malicious code or visit compromise websites inside virtual machines to observe their behavior and contain their impact.
One of the main goals of hypervisors like VMware Workstation is to create a barrier between the guest operating system that runs inside the virtual machine and the host OS where the hypervisor runs. That's why VM escape exploits are highly prized, more so than browser or OS exploits.