Microsoft's new Windows 10 19H1 test build paves the way for new Sandbox feature

Microsoft's latest Windows 10 19H1 test build includes one of the very few major new features revealed so far by Microsoft. That feature, Windows Sandbox, is a containerized desktop environment that allows users to run potentially suspicious applications in isolation.

Build 18305 of Windows 10 19H1, which Microsoft is rolling out to Fast Ring testers on December 19, includes support for this sandbox feature. Microsoft has been testing this feature privately for months, back when it was known as "InPrivate Desktop," and before that, by its codename, "Madrid."

In addition to adding sandbox support, today's test build enables the set up and sign-in process for Windows 10 with a phone number account that skirts the need to create a password. Those with Microsoft acounts with their phone numbers included can use an SMS code to sign in and set up an account on Windows 10. Once that's set up, users can opt for Windows Hello Face, Fingerprint or PIN to sign in.

Build 18305 adds Tamper Protection, a new setting from Windows Defender Antivirus, in the Windows Security app. It also includes a new "Protection History" experience, via which users will continue to see detections by Windows Defender Antivirus, but updated with more detailed and easier-to-understand information about threats and available actions. Controlled folder access blocks are now part of history, as are any blocks made through organizational configuration of Attack Surface Reduction Rules. 

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Today's test build also includes a simplified Start layout for new devices, new user accounts and clean installs. The new layout is a single column with reduced top-level titles. Microsoft officials said that commercial and education users also will be getting simplified layouts tailored to their own scenarios. 

There are a number of known issues with today's build, particularly around Windows Sandbox. Testers should read today's post for a full list. There are also a lot of other incremental new features, fixes and updates, also listed in today's blog post.

Today's test build is the last new Windows 10 19H1 release that Microsoft is planning to deliver to Insider testers, officials said.

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