Apple has pushed two updates today, to the data files used by XProtect, bringing its version number to 2129 dated 20 August 2020, and to its malware removal tool MRT, bringing it to version 1.66, also dated 20 August 2020. Note that MRT 1.65 doesn’t appear to have been distributed, and the previous version was 1.64.
Apple doesn’t release information about what these updates add or change, and now obfuscates the identities of malware detected by XProtect using internal code names.
Examination of the Yara file shows this brings several changes to XProtect’s detections. These include the substitution of a new signature for MACOS.44db411, and changes in the detection signatures of MACOS.7f5b902, MACOS.a291b70 and MACOS.30445d1.
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, Catalina and Big Sur, 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.