As explained in Section 3.1, a database of encrypted passwords
is stored in every Unix machine. A well known Unix program, called crack, is
available. This program uses information about poor choices of passwords, such
as using dictionary words for passwords, to attempt to decrypt the passwords in a password
database. Such passwords may then be used to gain unauthorized access to the
machine. Intruders often use guest accounts to gain access to the encrypted
password database, move it to another machine, and then execute crack to
gain access to authorized system accounts. System administrators regularly use the
crack program on their systems to determine which users have crack-able passwords.
Passwords which do not use dictionary words and which use a mixture of letters,
numbers and special symbols are more difficult to crack.