UAC was simultaneously seemingly ubiquitous and not a particularly "scary" warning. It just sounded like bland computer jargon to the uninformed. I was envisioning something like the https warnings that Chrome gives: a clear warning sign that uses emotionally loaded terms like "go back to safety" and hides the proceed link under the fold.

That being said, it's entirely possible that I'm overestimating the intelligence of the average user and that many of them wouldn't blink even in the face of a warning made up to look scary.