All network operating systems (NOS) must provide some measure of security to protect the network from unauthorized access. Hacking seems to be the national pastime these days. With most computer networks connected to the Internet, anyone anywhere in the world can and probably will try to break into your network.
The most basic type of security is handled through user accounts, which grant individual users the right to access the network resources — and govern what resources each user can access. User accounts are secured by passwords; therefore, good password policy is a cornerstone of any security system.
Most network operating systems let you establish password policies, such as requiring that passwords have a minimum length and include a mix of letters and numerals. In addition, passwords can be set to expire after a certain number of days, so users can be forced to frequently change their passwords.
Most network operating systems also provide for data encryption, which scrambles data before it is sent over the network or saved on disk, and digital certificates, which are used to ensure that users are who they say they are and files are what they claim to be.