ATLANTA—Microsoft has announced that the next major update to Windows 10 will run its Edge browser in a lightweight virtual machine. Running the update in a virtual machine will make exploiting the browser and attacking the operating system or compromising user data more challenging.

Called Windows Defender Application Guard for Microsoft Edge, the new capability builds on the virtual machine-based security that was first introduced last summer in Windows 10. Windows 10's Virtualization Based Security (VBS) uses small virtual machines and the Hyper-V hypervisor to isolate certain critical data and processes from the rest of the system. The most important of these is Credential Guard, which stores network credentials and password hashes in an isolated virtual machine. This isolation prevents the popular MimiKatz tool from harvesting those password hashes. In turn, it also prevents a hacker from breaking into one machine and then using stolen credentials to spread to other machines on the same network.

The Edge browser already creates a secure sandbox for its processes, a technique that tries to limit the damage that can be done when malicious code runs within the browser. The sandbox has limited access to the rest of the system and its data, so successful exploits need to break free from the sandbox's constraints. Often they do this by attacking the operating system itself, using operating system flaws to elevate their privileges.

Credential Guard's virtual machine is very small and lightweight, running only a relatively simple process to manage credentials. Application Guard will go much further by running large parts of the Edge browser within a virtual machine. This virtual machine won't, however, need a full operating system running inside it—just a minimal set of Windows features required to run the browser. Because Application Guard is running in a virtual machine it will have a much higher barrier between it and the host platform. It can't see other processes, it can't access local storage, it can't access any other installed applications, and, critically, it can't attack the kernel of the host system.

In its first iteration, Application Guard will only be available for Edge. Microsoft won't provide an API or let other applications use it. As with other VBS features, Application Guard will also only be available to users of Windows 10 Enterprise, with administrative control through group policies. Administrators will be able to mark some sites as trusted, and those sites won't use the virtual machine. Admins also be able to control whether untrusted sites can use the clipboard or print.

Microsoft recognizes that this feature would be desirable on consumer machines, too, and not just for Edge. Other browsers such as Chrome would also benefit from this kind of protection. So too would Office's "Protected Mode" that's used for opening documents from untrusted sources.

However, doing this has certain complexities. Currently, virtualized sites can't store persistent cookies, for example, because virtual machines get destroyed when the browser is closed. This may be acceptable for a locked-down enterprise environment, but it isn't a good fit for consumers.

There are also compatibility constraints. VBS installs the Hyper-V hypervisor. This requires a processor with hardware virtualization support, and it also requires I/O virtualization (such as Intel's VT-d) to protect against certain known attacks. This means that some systems in the wild won't support it. There are also software concerns; only one hypervisor can be installed at a time, which means that a machine that's running Hyper-V cannot also run VMware Workstation or Virtual Box, say, or software that uses virtualization behind the scenes, such as the Bluestacks Android-on-Windows software.

This virtualization also likely comes at some performance cost, although Microsoft is not saying just what that performance cost is right now.

Nonetheless, this use of virtualization to harden a system is an exciting move. Experimental and special-use systems such as Qubes OS have used virtualization in a similar way, but are far from mainstream offerings. Microsoft is uniquely positioned take this kind of capability mainstream.

Application Guard will become available later this year in Insider builds of Windows, hitting a stable version some time in 2017.