What is the security of a network?

It is security of network to prevent unauthorized accesss from tampering with the system.It is used for the protection of data or to protect your privacy form peoles who try to access your data.
It could be :
to prevent unauthorized persons from tampering with the system
secure data by predicting failures
to guarantee the non-interruption of a service

Causes of insecurity

There are usually two types of insecurity:

The active state of insecurity ,the user's lack of knowledge of the system's functionalities, some of which may be harmful to him (for example the non-deactivation of unnecessary network services to the user )
the passive state of insecurity , that is to say when the administrator (or the user) of a system does not know the safety devices he has at his disposal.

The purpose of the attackers

The motivations of the aggressors who are commonly known as "pirates" can be multiple:

• The attraction of the forbidden
• The desire for money (to violate a banking system for example)
• The need for fame (impress friends)
• The urge to harm (destroy data, prevent a system from working)

Abuse process

The goal of the attackers is often to take control of a machine in order to perform the actions they want. For this there are different types of ways:

• Obtaining useful information to carry out attacks
• Use the flaws of a system
• The use of force to break a system
• How to protect yourself?
• Keep yourself informed
• Know the operating system
• Reduce network access (firewall)
• Reduce the number of entry points (ports)
• Define an internal security policy (passwords, launch executables)
• Deploy security utilities (logging)

Source: Security