I forget the exact course of action, but from what I remember:
- ~/Library/LaunchAgents/com.microsoft.update.agent.plist
- ~/Library/Application\ Support/Microsoft\ AU\ Daemon/
- /Library/Application\ Support/Microsoft/MAU2.0/Microsoft\ AutoUpdate.app
Nuke all of that, though for the last one you may have to chmod 000 it.
Then do a search for everything with Microsoft Update in it and delete that too.
This process kind of reminds me of removing spyware infestations from Windows XP.
$ mdfind [thing]
$ mdfind microsoft
I usually pipe it into a text editor (mdfind 1password | subl), use my editor to put rm or so rm at the beginning of each one, then paste it into terminal to run. That lets me audit the files first as opposed to xargs but I'm sure there's a million ways—the point is mdfind can be useful.
If you can't drag and drop an end user application into the Applications folder and have it work, just find another option in the same software category.
The exception would be system utilities that modify the OS.
It's perfectly normal for those to require administrative permission to install.