After an attacker has performed enumeration, he or she can begin actually attacking the system. Enumeration has provided details that are actionable for the next phase of system hacking, including details of user accounts and groups. The information on usernames and groups provides points on the target system on which to concentrate the system hacking activities. Up to this point, progressively more detailed information has been gathered and what those services are offering has been determined; now the process of exploiting what has been uncovered can begin.

One of the most useful pieces of information discovered during the enumeration phase is a list of usernames. The information on user accounts provides the system hacking process a point to focus on using a technique known as password cracking. Password cracking is used to obtain the credentials of an account with the intent of using the information to gain unauthorized access to the system as an authorized user.

To understand why password cracking is successful, think of how and why organizations use passwords. Passwords are designed to be something that an individual can easily remember and at the same time not be something easily guessed, but there is the problem. In practice, individuals will tend to use passwords that are easy to guess or susceptible to cracking methods such as those introduced in this section. Some examples of passwords that lend themselves to being compromised through cracking include the following:

• Passwords that use only numbers

• Passwords that use only letters

• Passwords that are only upper- or lowercase letters

• Passwords that use proper names

• Passwords that use dictionary words

• Short passwords (fewer than eight characters)

Passwords that adhere closely to any of the points on this list lend themselves to quick and easy password cracking methods. Passwords that avoid any of these points tend to be somewhat harder to crack, but not impossible, as the techniques discussed in this section will demonstrate.