shadow password

Normally, each user's password is stored, encrypted, in the file /etc/passwd. This file must be readable by all users so that certain system functions will operate correctly. However, this means that copies of user's encrypted passwords are easily obtained, making it possible to run an automated password-guessing program against them. Shadow passwords, on the other hand, store the encrypted passwords in a separate highly-protected file, making it much more difficult to crack passwords.