In addition to the Catalina 10.15.1 and Security Updates, Apple has pushed another update today, to the data files used by XProtect, bringing its version number to 2107, dated 29 October 2019. Those updating to Catalina 10.15.1 will find this update part of the whole macOS update, and it doesn’t have to be downloaded separately.
Apple doesn’t release information about what this update adds or changes. This doesn’t appear to bring substantial changes, only minor refinements to some of the existing ‘yara’ definitions.
You can check whether this update has been installed by opening System Information via About This Mac, and selecting the Installations item under Software.
A full listing of security data file versions is given by SilentKnight, LockRattler and SystHist for El Capitan, Sierra, High Sierra, Mojave and Catalina, available from their product page. If your Mac has not yet installed this update, you can force an update using SilentKnight, LockRattler, or at the command line.
I have updated the reference pages here which are accessed directly from LockRattler 4.2 and later using its Check blog button.
Thanks to Al for checking the content of this update.