According to Gabriel Aul, a security update to the current build of the operating system will not install if a user has Office already installed. Aul, one of the most prominent members of the Windows 10 team, users might have to reinstall Office.
Users of build 9879 of Windows 10, if they want to install the security fix, may have to uninstall Office, and later reinstall it. Aul tweeted about it earlier as well:
Microsoft will not be releasing a new build of Windows 10 this year, but smaller updates will be rolled out. Windows 10 will bring all screen sizes, form factors, and app environments for Microsoft if it pulls off its larger vision. The company will unveil a new, consumer-focused version of Windows 10 in January that may detail how the code will handle switches between user input sources