Interesting how it gives an alert after a day and not immediately - the realtime protection doesn't detect anything and what I think is happening is the scheduled startup scan is detecting it instead as it scans through.
I can download the dmg without warning, open it without warning... It's only when I set a custom scan on the dmg or leave it on the Mac to let the scheduled scan run that it either comes up with this window, or just logs with 2 infected files and nothing actually done.
Also find it strange that it can't be moved to quarantine either...
scan.jpg
The same thing happened to me, too. You are right, it's kinda interesting.