If you reset your router, or your ISP fails to provide a stable connection and your internet crashes, your IP probably changes and will count as if 'someone logged with your account' from a different place(IP). It happened to me a lot when I had a crap net and my connection would crash a lot, I had to keep changing my password almost everyday. Now it only happens when my ISP messes up and I lose my connection (has only happened like once a month). Sometimes it even could happen when you're sleeping and you didn't notice your net crashing.