Internet Security Systems                          
1- Introduction :Nowadays, almost every home has at least one computer, either desktop or laptop. Most of them have internet connection especially in developed countries. A computer is not a luxury need for people anymore as it used to be back in 1970s. One can get a computer that has more power, performance, memory, and disk storage than a computer bought in 1980s. Thanks to the technologies used to build the computer and the innovations in computer design that make this possible. The nature of computing has been changed over the last few years. As computers have become cheaper and more powerful, the more people are able to buy a computer. Many companies start depending on computers to do their business. Unfortunately, these changes also have disadvantages. One of the negative effects of these changes is computer crime has became a serious threat to home user and companies. One of the biggest crimes is phishing. 2- Computer virus:A virus is a type of program that can replicate itself by making copies of itself, which can be possibly modified. The main criterion for classifying a piece of executable code as a virus is that it spreads itself by means of ‘hosts’. A virus can only spread from one computer to another when its host is taken to the uninfected computer, for instance by a user sending it over a network or carrying it on a removable medium. Additionally, viruses can spread to other computers by infecting files on a network file system or a file system that is accessed by another computer.  2.1- Computer virus damage:The damage that computer virus can inflict on system are : 2.1.1-Some viruses can delete or change files. Some viruses will delete all of the documents, or even reformat the hard drive, making the computer unusable. 2.1.2- Some viruses can release confidential information like credit card information, account numbers, and passwords by emailing it to random email addresses or the address of the virus writer. 2.1.3- Some viruses can slow down the system dramatically. 2.1.4-Some viruses plant monitoring software or change security settings that allow hackers to enter the computer without the knowing of user about it and steal information or control it. 2.2-the security measures that are commonly implemented to safeguard against computer viruses :So we need antivirus software to make the computer safe. Once we’ve installed the antivirus software, we will need to download regular updates that tells the antivirus software about new viruses and how to detect them. Most antivirus software comes with a year’s worth of updates, and we can usually set the software to either automatically download the updates, or  we will display a reminder for recognize us. And this is the computer virus and how it can damage the computer system and how we can protect us from this.  3- Computer worm:which is a self-replicating computer program, similar to a computer virus. A virus attaches itself to, and becomes part of, another executable program; however, a worm is self-contained and does not need to be part of another program to propagate itself. They are often designed to exploit the file transmission capabilities found on many computers. The main difference between a computer virus and a worm is that a virus cannot propagate by itself whereas worms can and it has the ability to copy itself from machine to machine. Worms normally move around and infect other machines through computer networks. Using a network, a worm can expand from a single copy incredibly quickly. For example, the Code Red worm replicated itself over 250,000 times in approximately nine hours on July 19, 2001. A worm uses a network to send copies of itself to other systems and it does so without any intervention. computer worms tunnel through computer’s memory and hard drive. 3.1- Computer worm damage :It does not alter any files on machine. However, worms can still cause havoc by multiplying so many times that they take up all your computer’s available memory or hard disk space. If a worm consumes the memory, the computer will run very slowly and possibly even crash. If the worm affects the hard disk space, the computer will take a long time to access files and the user will not be able to save or create new files until the worm has been eradicated. also the payload of the worm will destroy any file with the extension .h, .c, .cpp, asm, .doc, .ppt, or .xls on our hard drives, any mapped drives. 4- Computer hacking :Unauthorized access to computer systems, either for fun or for malicious or fraudulent purposes. Hackers generally use computers and telephone lines to obtain access. In computing, the term is used in a wider sense to mean using software for enjoyment or self-education, not necessarily involving unauthorized access 4.1- the ethical issues concerning computer hacking :People who use the computer to commit crimes, harass people, invade privacy, etc. are called “hackers.”  One of the most common forms of hacking in the education arena is “malware,” which is software designed by hackers to attack some part of a computer system.  According to Haag, Cummings, & Rea (2002), typical types of hackers who may be present in a school or institution are:  4.1.1-  White-hat hackers–after breaking into the system, they usually inform the victims 4.1.2- Black-hat hackers–are cyber vandals who deliberately cause trouble for people 4.1.3- Crackers–hackers for profit 4.1.4- Hacktivists–politically motivated hackers 4.1.5- Script bunnies–want to be hackers but don’t have the technical expertise   4.2- the fact that computer hackers are looked down upon from an ethical point of view :Respect for property and privacy is the last major issue concerning students.  Plagiarism is easier than ever because of computers. With the help of online services, students can download information, such as term papers and personal statements, from the Internet for a fee. Although this is blatant plagiarism, many students use these services. Now students also have the luxury of using electronic databases to conduct research.  While using these databases eliminates the need to spend hours in the library, it also allows students to cut and paste entire bodies of text into their paper with ease. Invading the privacy of others is a violation of the Constitution; however, people tend to believe that it does not apply to cyberspace.  Accessing another person’s materials online is a form of privacy invasion. Gaining unauthorized access to other people’s electronic mail or accessing files by breaking passwords is an invasion of privacy, and thus unlawful.  Some students take it a step further by destroying intellectual property once they illegally access it.  Deleting a file or erasing a disk constitutes destruction of property.  Although this property is in “virtual space,” it is unethical as well as unlawful. 5-firewall :A system designed to prevent unauthorized access to or from a private network. Firewalls can be implemented in both hardware and software, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria.  5.1- the Application Layer Firewall :In computer networking, an application layer firewall is a firewall operating at the application layer of a protocol stack. Generally it is a host using various forms of proxy servers to proxy traffic instead of routing it. As it works on the application layer, it may inspect the contents of the traffic, blocking what the firewall administrator views as inappropriate content, such as certain websites, viruses, attempts to exploit known logical flaws in client software, and so forth. An application layer firewall does not route traffic on the network layer. All traffic stops at the firewall which may initiate its own connections if the traffic satisfies  5.2-the Network Layer Firewall in your report :In computer networks, a network layer firewall works as a packet filter by deciding what packets will pass the firewall according to rules defined by the administrator. Filtering rules can act on the basis of source and destination address and on ports, in addition to whatever higher-level network protocols the packet contains. Network layer firewalls tend to operate very fast, and transparently to users. 6-conclusion :Finally The computer crimes have increased rapidly along with the growth of computer. One of the biggest crimes is phishing. This practice has caused a lot of loss in financial to both user and business and i have talked about the factors of  internet security system such as virus and how it damage the computer system and how we can protect our computers from this, the worm and it’s damage, the computer hacking and it’s ethical issues and the firewall and it’s  Application Layer Firewall and Network Layer Firewall.