GateKeeper, MRT (Malware Removal Tool), and XProtect are all built-in features of macOS designed to prevent malware threats and other nefarious software from being installed or used on a Mac. These security features exist in the background and are updated with regular system software updates to macOS, but Apple will also push quiet updates to xprotect or MRT to add new definitions and block newfound threats.
Advanced users may wish to know what versions of those security tools is installed on a Mac. WatchDog is a lovely script written for that.
$ ./watchdog.swift
Name Date Version
---------------------------------------------------------
XProtect 23 Feb 2017, 10:34 AM 2089
Gatekeeper 11 Aug 2016, 10:08 AM 94
SIP 31 Jul 2016, 3:21 AM 14.0
MRT 15 Oct 2016, 10:57 AM 1.7.1
Core Suggestions 08 Otc 2017 10:22 PM 788
Incompatible Kernel Ext. 18 Dec 2016, 8:54 AM 12.5.0
Chinese Word List 13 Otc 2014 8:22 PM 4.22
Core LSKD (dkrl) 18 Feb 2017, 6:17 AM 8
Torin Kwok.