When you sign in to your Microsoft account, you might see the following error message:
"Microsoft account passwords can contain up to 16 characters. If you've been using a password that has more than 16 characters, enter the first 16."
This doesn't mean that your password has been shortened. Actually, Windows Live ID passwords were always limited to 16 characters—any additional password characters were ignored by the sign-in process. When we changed "Windows Live ID" to "Microsoft account," we also updated the sign-in page to let you know that only the first 16 characters of your password are necessary.
To avoid this error message in the future, you only need to enter the first 16 characters of your password.