Build 4266.1001 is pre-Patch Tuesday, October 2015. It is vulnerable to:
It contains the core codebase before any subsequent monthly quality updates or feature variations changed the architecture. Microsoft Office 2016 Pro Plus 16.0.4266.1001 V...
If you suspect you have the 16.0.4266.1001 build: Build 4266
Office 2016 Pro Plus represents the pinnacle of Microsoft’s “perpetual license” model before the full push to Microsoft 365. Version 16.0.4266.1001 is a stable, post-update build that irons out many early bugs. It’s aimed at businesses and professionals who need the full desktop apps without a subscription. Build 4266.1001 is pre-Patch Tuesday
: Includes Word, Excel, PowerPoint, Outlook, OneNote, Publisher, Access, and Skype for Business.