Warning: Today's Windows 10 Security Update Has a Known Conflict with Office

Microsoft's Gabe Aul just tweeted a warning about one of the security updates due to come down the Automatic Update chute in a few hours. Unfortunately, he didn't mention the update by name, and he didn't describe the symptoms, but he did give a workaround.
If you are running Windows 10 Tech Preview build 9879 (almost all of you Windows10 testers are on build 9879), and you have Office installed on your machine (not clear which version/s of Office), heed Aul's advice.
Here's what he tweeted: