Apple has pushed two updates today, to the data files used by XProtect, bringing its version number to 2110, dated 12 December 2019, and to its malware removal tool MRT, bringing it to version 1.51, also dated 12 December 2019. Only Catalina received the XProtect version 2109 update, which wasn’t released for earlier versions of macOS.
Apple doesn’t release information about what these updates add or change, and now obscures the identities of malware detected by XProtect using internal code names.
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.
I maintain lists of the current versions of security data files for Catalina on this page, Mojave on this page, High Sierra on this page, Sierra on this page, and El Capitan on this page.