It's even more interesting when you start the observation at the stage of downloading the software in question.

I saw it with some co-workers - first google result, obviously fake colorful download buttons, ads everywhere and they finally have an (not necessarily the correct) install.exe they wouldn't think twice about actually executing it. Now imagine doing the same thing with less specific search terms like "mp3 converter" instead of Skype, VLC or Dropbox. That's a very sure way for non-technical users to mess up their system.