A system will be particularly vulnerable to this type of an attack if it does not have a proper enforcement mechanism in place to ensure that passwords selected by users are strong passwords that comply with an adequate password policy. In practice a pure brute force attack on passwords is rarely used, unless the password is suspected to be weak. Other password cracking methods exist that are far more effective (e.g. dictionary attacks, rainbow tables, etc.). Knowing the password policy on the system can make a brute force attack more efficient. For instance, if the policy states that all passwords must be of a certain level, there is no need to check smaller candidates.