A hack is when someone takes control of your computer, personal details or so on. I.e, "that businesses website was hacked by hackers who deleted the entire site"

Somewhere, probably around the mainstream "L33T" talk era, it started being used to describe tips. I guess it's a non literal use of a word with a different meaning. Terms like "lets BEAT this" existed way before and the BEAT part of it isn't as in literally beating. Someone just thought it's a way to describe something in a dramatic way, i.e not to pass somethng, but to BEAT or SMASH. 

The word TIP just doesn't have much of an impact, HACK is a much stronger word. So I think that stronger word nature puts more emphasis on it being a bigger thing that it is. Again, i.e... "Here's a quick tip... yada yada"... or... "Here's a hack", hack makes it sound much better than something being a tip.