I had the same thing happen to me once a while back. I logged in I noticed I had someone else account. Only reason I knew wasn't my account was the miles. It was an extremely large balance. I was like whoa!!! I hit the jackpot!!! How did I get so many miles?... but then I saw the name and stuff. I was able to go through all their stuff. I logged out and logged back in and it was all back to normal. But it was shocker when I first saw someone else information.