The Malicious Software Removal Tool (MRT) scans for popular infections and if any detected then they are removed. It is a run-once tool, so it doesn't reside in memory and monitor the system like MS Windows Defender.
The tool is updated every month and if using
Automatic Update, then it will automatically download the update and scan the computer every month.
When running %windir%\System32\Mrt.exe a log is created (%windir%\Debug\Mrt.log), where actions and errors can be seen.