C:\Windows\debug\mrt.log
を確認してください。
以下のようなログが残っているでしょう。
---------------------------------------------------------------------------------------
Microsoft Windows Malicious Software Removal Tool v5.68, January 2019 (build 5.68.15555.1)
Started On Thu Jan 17 09:00:09 2019
Engine: 1.1.15500.2
Signatures: 1.283.998.0
MpGear: 1.1.15201.1
Run Mode: Scan Run From Windows Update
Results Summary:
----------------
No infection found.
Successfully Submitted Heartbeat Report
Microsoft Windows Malicious Software Removal Tool Finished On Thu Jan 17 09:07:24 2019
Return code: 0 (0x0)
Hebikuzure aka Murachi Akira