1. Upon relaunching MacUpdate Desktop, I had to (re)install my SN & PW. Also, I had to reset a few options/selections. AFAIK, all is (again) normal in that regard.
FWIW, MacUpdate "claims" the nefarious wrapper is not in play for registered MU Desktop users (though I'm not convinced, so I go directly to the developer's site).
Since MU checks for outdated apps upon launch, maybe that's related... (Emphasis added)
~/Library/LaunchAgents/com.macupdate.desktop5.scanner.plist certainly seems to fill that bill...deliberate on your part as I guessed it might be.
Your other item may remain a mystery forever.
Edit: Out of curiosity, did you ever install anything that enabled you to view attachments sent by an Outlook user?