Network security in computer networks is essential to monitor network access and prevent misuse of network resources that are not valid. The task of network security is controlled by the network administrator.
There are two main elements forming the network security:

Security wall

both physical and virtual, which is placed between the device and network service which is used and those who would do evil.

Security plan

which will be implemented in conjunction with other users, to keep sistemtidak impenetrable from the outside.

Advanced Computer Networks

• Security Plan, which will be implemented in conjunction with other users, to keep sistemtidak impenetrable from the outside. Defined security aspects of this fifth point.

a. Confidentiality, Require that information (data) can only be accessed by those who have the authority.

b. Integrity
Requires that information only dapatdiubah by the party who has the authority.
c. Availability
Requires that information available to the parties who have authority when needed.

d. Authentication
Suatuinformasi requires that the sender can be identified correctly and there is no guarantee that a false identity is not obtained.

e. Nonrepudiation
Pengirimmaupun requires that both recipient information can not deny sending and receiving messages.
Attack (interference) to the security can be categorized into four main categories:

a. Interruption An asset of an attacked system so that it becomes unavailable or can not be used by the authorities. An example is the destruction / modification of the hardware or network channels.

b. Interception An unauthorized person to gain access to an asset. The parties in question can be a person, program, or other systems. An example is the interception of data in a network.

c. Modification An unauthorized person can make changes to an asset. An example is the change in the value of the data file, modify the program so it goes wrong, and the modification of the message being transmitted in the network.

d. Fabrication An unauthorized party inserts a fake object into the system. An example is sending a false message to others.

There are several principles that need to be avoided in dealing with security issues: silent and all will be fine hiding and they will not be able to find you the technology used complex / complicated, meaning safe

Definition of Network Security is to keep the resource being used properly by privileged users. Computer network security itself is often seen as a result of several factors. This factor varies depending on the base material, but normally at least some of the following are included:

• Confidentiality 
• Integrity 
• Availability 

Network security also have factors that make a network at risk for data loss. Some Causes Risk factors In Computer Networking is as follows:

• Human weakness (human error)
• Weakness hardware ber komputerai
• Weakness network operating system
• The weakness of the communication network system

Computer Network Threats

• PHYSICAL
  • Theft of computer hardware or network device
  • Damage to the computer and network communication devices
  • Wiretapping
  • Catastrophe
• LOGIK
  • Damage to the operating system or application
  • Virus
  • Sniffing

One network security threats is Hacker. The term Hacker Hacker emerged in the early 1960s among members of student organizations Tech Model Railroad Club at the Artificial Intelligence Laboratory of the Massachusetts Institute of Technology (MIT). The student group tersebutmerupakan one of the pioneering development of computer technology and they operate with a number of mainframe computers.

The word hacker first appeared in a positive sense to refer to a member who has expertise in the field of computer and able to make computer programs better than has been designed together. Then in 1983, growing hacker analogy to refer to someone who has an obsession to understand and master the computer system. Because, in that year for the first time the FBI arrested a group of computer criminals 414s based in Milwaukee USA. 414 is their local area code.

The group then called hackers are convicted of burglary 60 computers, from computers owned by Cancer Center Memorial Sloan-Kettering to a computer owned by Los Alamos National Laboratory. One of the perpetrators enjoy immunity as testimonial, while five other players get probation.

Then on the next development emerged another group who mention themselves hackers, but it's not. They are (especially the men) who got the satisfaction of breaking through computer and telephone outsmart (phreaking). Real hackers call these people 'Cracker' and does not like to hang out with them. True hackers looking kracker as lazy, irresponsible, and not very smart. Real hackers do not agree to say that the person through the security has become a hacker.

The hackers had a meeting once a year is held every mid-July in Las Vegas. Event the world's largest hacker gathering is called Def Con. Def Con event to event is the exchange of information and technology related to hacking activities.

The conclusion of the differences hackers and crackers are:

Hacker

• People who secretly studied systems that are usually difficult to understand and then manage it and to share the results of tests done.
• Hackers do not damage the system

Craker

• People who secretly studied the system dengam evil intent
• Arises because human nature always want to build (one of them damaging)

The terms on the hacker:

• Mundane: know about the hacking but do not know the methods and processes.
• lamer (script kiddies): Try scripts ever created by hacking activists, but do not know how to make it.
• wannabe: little understood methods of hacking, and has begun to successfully break through so berfalsafah; HACK IS MY RELIGION
• larvae (Newbie): newbie hacker, hacking techniques began mastered well, often experimenting.
• hacker: hacking activity as a profession.
• wizard: hackers who create learning communities among them.
• master teacher of the master hacker: more leads to the creation of "tools hacker tools" powerful that one can support the activities of hacking, but more so a common system programming tools.