Following yesterday’s pushed update to XProtect, Apple has overnight pushed an update to its malware removal tool MRT, bringing it to version
1.30. Apple doesn’t release any information about such updates, which presumably extends the range of malware which the tool can remove.
Rummaging around in the strings contained in MRT suggests that it can now remove the same mysterious OSX.28a9883 (variant A) which XProtect can now detect. Additionally, there is mention of MinerGate bitcoin-mining software, which might be a part of OSX.28a9883 or other malware which MRT can remove. I’m afraid that there is still no further information about other, more widely-used names for what Apple calls OSX.28a9883.
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 LockRattler and SystHist for El Capitan, Sierra and High Sierra, available from Downloads above. If your Mac has not yet installed this update, you can force an update using LockRattler, or at the command line.