I had someone access my Origin account, it was from 2009 with the same password for years, likely I used the same password and login in some forum that got hacked and the passwords/logins leaked,
I had the warning of someone else was using my account a few times, sadly when I tried to change my password I noticed that I had one of those secret questions and couldn't remember the answer, so I checked the option to require a email code to login I think (it didn't require me to give the answer for this change), and I started to get those emails from the other person trying to use it... later I remembered the secret answer and also managed to change the password, but I still got a password change request not made by me later... but since they didn't control my email no worries...
the worst thing would be if someone manages to get your login+password and your email password, so make sure you have different passwords on as many things as possible.