Microsoft has made available Intel microcode updates (firmware), initially for some Skylake devices running the most broadly installed version of Windows 10 - the Windows 10 Fall Creators Update - through the Microsoft Update Catalog, KB4090007.
The update covers systems based on the Intel Skylake H/S, U/Y U23e 6th Generation Intel Core processors, and it is standalone update available through the Microsoft Update Catalog and targeted for Windows 10 version 1709 (Fall Creators Update) & Windows Server version 1709 (Server Core). This update also includes Intel microcode updates that were already released for these Operating Systems at the time of Release To Manufacturing (RTM).
Microsoft will will offer additional microcode updates from Intel for more Operating Systems as they become available to Microsoft. You can find more information and a table of updated Windows editions in the Windows customer guidance article.
Microsoft has also been working with anti-virus (AV) partners on compatibility with Windows updates, resulting in the vast majority of Windows devices now having compatible AV software installed. The focus of this work is to manage the risk of compatibility issues, especially those that result from AV software that makes unsupported calls into Windows kernel memory. Due to this potential risk, Microsoft requires that AV software is up to date and compatible.