If you change the Microsoft account password online and don’t change the password on the phone, the phone features will show an authentication error either immediately or after a delay:Features where a delayed error occursPrimary Microsoft account use and sync experiences (email, people, calendar, SkyDrive, chat, etc.) usually have a cached auth token that can take up to 8-to-12 hours to expire. Once it does, those experiences will begin to fail and a generic password failure is shown.Features where an immediate error occursPrimary Microsoft account experiences that need fresh auth, such as Store purchases and downloads will fail immediately and a generic password failure is shown.If concerned about security in case of a lost or stolen phone, it is recommended to set a password for the lock screen. You may also consider using the Find My Phone functionality on WindowsPhone.com to map, lock, or even erase the phone.