I'm not proud of this but this is what I did about 16 years ago:
Guy in office gives me his external drive for virus scanning.
I open the drive to take a cursory look at what it contained. There was work stuff and there was a movies/TV series folder downloaded from torrents. Size was tons of gigs (more than 20GB if I recall correctly). I figured it would be awkward asking him if I could copy that folder (hey, what you doing looking at my folders for. I gave it to you for virus scanning!)
So I make a batch file:
@ECHO off
echo Scanning for viruses...
(silent copy his torrents folder to my laptop HDD with xcopy)
He kept checking back from time to time and I kept showing him the CMD window with that message.
When the copying was done, I used a command line virus scanner (I think Sophos) to do a quick scan of his drive which took maybe 10 minutes.
Most fruitful IT work ever!
