Microsoft today took the unusual step of telling users running Windows 10's Technical Preview to uninstall Office before applying one of December's security updates.

"We just made a tough call after working through the night that I thought I should share with you," wrote Gabe Aul, the engineering general manager for Microsoft's operating system group, in a four-part Twitter understatement Tuesday.

"We have a security update going out today, and the installer fails on 9879 if Office is installed," Aul continued. "Rather than rolling a new fix (losing several days in the process) we're going to publish it as is. The workaround is painful: uninstall Office, install the hotfix, reinstall Office. Sorry. We're working hard to fix."

Aul's mention of "9879" referred to the latest "build" of the preview; Microsoft issued Build 9879 four weeks ago.