Base System DMG opening without user action

Something strange hast just happened… I had to burn some files on a a DVD for a family member and so my 2012 Mac mini was happily doing this. Then when I looked at the screen, I saw - just for a second - the dialog one gets while opening a downloaded dmg file (the one where it basically opens the virtual disk). I could just read something like “Opening BaseSystem.dmg”.

Has anyone an idea what this was? I’m concerned right now that there might be some malware at play here…

I think BaseSystem.dmg is used by Mac OS X to apply things like firmware updates which can be downloaded automatically in the background.

There’s a thread here about others who have seen the same thing, which might be helpful too:

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