About three years ago, my Gmail was hacked (or illegally accessed by someone else). One day I logged into Gmail and got an ominous warning at the top of my Gmail box that said my Gmail account had been accessed from an unknown IP address and that I should check it out. And, sure enough, there was a listing of a strange IP address (located in Florida, which is not where I live). I'm not sure who was looking in my Gmail account but it was a frightening experience.
I don't know how they got into my Gmail. I have a theory but no proof. I changed my password on my Gmail, Paypal and bank account (as my Gmail was the primary email for all those accounts at the time). No other accounts were accessed. So I'm hoping it was just a random occurrence.
I'm not sure if anyone else had this happen but it can be very disconcerting, thinking that a stranger is reading through your emails.