password

A security method that identifies a specific, authorized user of a computer system, a network, or a resource by a unique string of characters.

In general, passwords should be a mixture of upper- and lowercase letters and numbers and should be more than six characters. Here are some general guidelines:

Passwords should be kept secret and changed frequently. The worst passwords are the obvious ones: people's names or initials, place names, phone numbers, birth dates, and anything to do with computers or Star Trek. There are a limited number of words in the English language, and it is easy for a computer to try them all relatively quickly.
Change all passwords every 90 days, and change those associated with high-security privileges every month. Some network operating systems require that passwords expire even more frequently. For example, in NetWare 5, passwords expire after 40 days by default.
Some systems provide default passwords, such as MANAGER, SERVICE, or GUEST, as part of the installation process. These default passwords should be changed immediately.
Limit concurrent sessions to one per system.
Do not allow more than two or three invalid password attempts before disconnecting.
Do not allow generic accounts.
Promptly remove the accounts of transferred or terminated people, as well as all unused accounts.
Review the security log files periodically.