Apple has just pushed the first updates of 2018 for two of the security tools built into OS X El Capitan, and macOS Sierra and High Sierra.
MRT version 1.28 is a full update to Apple’s Malware Removal Tool. As usual, Apple doesn’t provide any information on what has changed in this new version.
XProtect data files are updated to version 2098, which adds protection against OSX.Bundlore.D, a newer variant of an established AppleScript-based installer of adware and other unwanted material, and updates existing protection against OSX.HMining.D.
You can check whether these updates have 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 LockRattler and SystHist for El Capitan, Sierra and High Sierra, available from Downloads above.