Microsoft today released a new Windows 10 preview for PCs with Windows Defender Security Center and Windows Defender Firewall improvements. This build is from the RS5 branch, which represents the Windows 10 update the company plans to release later this year. The next update will come sooner (possibly as soon as next week), from the RS4 branch.

Windows 10 is a service, meaning it was built in a very different way from its predecessors so it can be regularly updated with not just fixes, but new features, too. Microsoft has released four major updates so far: November Update, Anniversary Update, Creators Update, and Fall Creators Update.

This RS5 build is for Windows Insiders who have chosen the Skip Ahead option, meaning they continue to receive builds from the RS_PRERELEASE branch. Only a small subset of Insiders can opt into Skip Ahead, as Microsoft still needs testers helping with RS4.

The Windows Defender Security Center (WDSC) has been updated to include Fluent Design elements. Spacing and padding have been adjusted — the categories on the main page should also adjust dynamically as more room is needed. WDSC even has a title bar so it can play nice with accent colors and Sets.

Speaking of Windows Defender, the Firewall now supports Windows Subsystem for Linux (WSL) processes. You can now add specific rules for a WSL process, just as you would for any Windows process, and receive notifications for it.

This desktop build also includes the following general bug fixes and improvements:

Fixed an issue where File Explorer would always open with the ribbon minimized, rather than remembering how you’d left it.

Fixed an issue where elements on the main page of the Windows Defender Security Center app would slightly change size on mouse hover.

Fixed an issue where non-default languages might unexpectedly have the option to remove in Settings greyed out.

Fixed an issue where the Color Filters and High Contrast icons were switched in Settings.

Fixed an issue where clicking links in Settings that launched other apps would result in Settings crashing and nothing else happening.

Fixed an issue resulting in some people experiencing a Settings crash when navigating to Apps > Default Apps > Set defaults by App.

Today’s update bumps the Windows 10 build number for the RS5 branch from 17643 (made available to testers on April 12) to build 17650.

This build has 12 known issues:

On resuming from sleep, the desktop may be momentarily visible before the Lock screen displays as expected.

When Movies & TV user denies access to its videos library (through the “Let Movies & TV access your videos library?” popup window or through Windows privacy settings), Movies & TV crashes when the user navigates to the “Personal” tab.

Tiling and cascading windows, including features like “View Side by Side” in Word, will not work for inactive tabs.

The Office Visual Basic Editor window will currently be tabbed but is not intended to be in the future.

Opening an Office document while the same app has an existing document open may cause an unintended switch to the last active document. This will also happen when closing a sheet in Excel while other sheets remain open.

Local files or non-Microsoft cloud files will not be automatically restored and no error message will be provided to alert the user to that fact.

Sets UX for Office Win32 desktop apps is not final. The experience will be refined over time based on feedback.

The top of some Win32 desktop app windows may appear slightly underneath the tab bar when created maximized. To work around the issue, restore and re-maximize the window.

Closing one tab may sometimes minimize the entire set.

An issue causes Narrator to read extra text when invoking Alt + Tab.

Using arrow and Page Up / Page Down keys doesn’t work to scroll webpages in Microsoft Edge. You’ll need to use another input method (mouse, touch, or touchpad).

If you complete the setup for a Windows Mixed Reality headset on this build, the headset will remain black until it is unplugged and reconnected to the PC.

As always, don’t install this on your production machine.