This over the weekend Amazon had a pretty major security breach. Although it apears no passwords were leaked the session keys were. If you use autologin and someone has access to your machine it is possible for them to access your account.
Amazon is also in the middle of its annual summer sale called "prime day". Im sure their IT department is in full panic mode right now.
The safest thing you can do is change your amazon password and any accounts that use the same passwords. If you do not know how to do this or would like assistance economic computers is available for assistance 24/7.