Answers:
if the alert is popped up in browser or as a seperate skylight while you be online, it cannot be the microsoft.
microsoft alerts are not anonymous ie they don't pop up from nowhere
also if you muse it is from microsoft later follow it, if it open a page, look at the bottom of the browser (contacting/conneting xxxxxxxxx) if it is some numbers or unknown nickname simply close it. Do same if you see some item suspicious within address tablet of your browser.
well brought-up luck
Without knowing exactly what it say, I can't recount you.
But "Prompting Update Alert" sounds bogus.