Probably my yahoo mail account. I’ve mostly transitioned off it, but a few things still come to it and it predates even my gmail account (which I barely ever use either). Apple ID’s Hide My Email ability has basically rendered all the other ones pointless though since I can just generate a new fake email address whenever I want to register for something fishy. I wish phone numbers worked the same way.
I have literally never downloaded pirated software since OS 9 went away and OS X became a thing. Open up your task manager and look at how many processes there are (Window, Mac or Linux) and ask yourself if you’re going to notice the one extra process that is out of place.
As for files with extra extensions, this is why you should always set Explorer/Finder/whatever to show all file extensions the very first thing, regardless of what OS you’re running too.