A Definition Of Computer Viruses Computer Science Essay

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A computer virus is a contagious program which can infect other programs by modifying to replicate itself or the environment without the acknowledgement of users. It travels with the programs that contain it and may cause damage to the completeness of stored data. Virus infection takes place when a user uses an infected program on a personal computer and spread to another. It may corrupt or delete data on a computer, use of an e-mail program to spread the virus to other computers, or even delete everything on the hard disk.

Specific Viruses

Generally there are three main classes of virus known as file infectors, system or boot-record infectors and macro viruses.

File infector

It is a computer program that modifies program files which are usually .EXE or .COM files and when the program runs, virus will start to activate and do whatever it wants.

System or boot-record infectors

It attacks the boot program that is stored on every bootable floppy disks or hard disks. When a computer is being started up, it allows the virus writers to install their program and thus allowing them to have a chance to take control over the systems.

Macro viruses

It makes use of the built-in programming languages in popular programs such as Microsoft Word and Microsoft Excel.

Other than the three main classes of virus, there are commonly three other types of computer virus known as Trojan horse, worm and key logging.

Trojan horse

It is a malware software that appears to perform a desirable function for the computer user but instead facilitates unauthorized access to the user's computer system. It allows hackers to gain access to the target computers and perform operations like getting passwords and credit card information.


It is a self-contained computer program that is able to spread its functional copies of its segments to other computer systems. It invades computer network and interfere with the host computer operation.

Key Logging (Also known as ‘keystroke logging’)

It is a software operates quietly to keep a record of the keys the users type then transmit the information to hackers. Hackers will then be able to obtain the computer user’s details of usernames and passwords used.

How It Spreads

Computer virus can be spread through three channels namely; floppy disk, network and internet. Infected files are stored in a removable medium such as floppy disk, CD, DVD, or USB drive and will be spreaded when it is opened to an uninfected personal computer. Virus spreads very fast to the other programs in the computer once infected files are shared through the network. Internet affects the most to the computer as viruses can appear in the form of web page, unknown emails and the attachments in emails. Therefore, users should not open attachments in emails unless one is expecting it. Viruses can appear in the form of videos, greeting cards or images. Computer users may open and without knowing that it contain virus, they send it to other users.

Viruses can be divided into two types based on their behavior when they are executed. Nonresident viruses search for new files to infect and transfer control to the application program they infected. Resident viruses do not search for hosts when they are start. They load into memory and transfers control to the host program and will infect new hosts when the files are accessed.

Areas Of Infection

If a computer is being attacked by virus, it can cause damage to the systems in hard disks, corrupts executable programs, files, can delete files and reformat hard disk in the computer. For serious cases, it may also affect the motherboard and can cause the computer to crash. When virus affects motherboard, there is no cure for it and users will have to replace the whole motherboard which will be equaled to replacing a computer.

Preventive Measures Against Virus

Prevention is better than cure but before taking preventive measures against virus, users have to take note of the symptoms in which users can detect for likely computer viruses. Computer will run slower, programs will not load properly, computer keeps restarting on its own, programs or files will get hanged on the same screen and error messages keep appearing.

To avoid computer being attacked by virus, preventive measures have to be taken. There is a need to make backup copies of important files regularly to prevent losing the entire data. Install and keep the anti-virus program updated in the computer to detect and destroy viruses. New viruses, worms and Trojans are developed all the time so this is to ensure that users are always being protected. Scan any new software for virus before installing to assure that you do not bring the virus into uninfected computer and to on firewall after computer is on.

Do not open attached files in emails that are from strangers or those with unfamiliar subject heading. Ignore unfamiliar websites that appears from user's contacts in the online chat room. Do not download files without much thinking. These may link to websites containing virus and lead to the spread of infection.

Possible Treatments If LAN Is Infected

If the Local Area Network (LAN) is infected, the first thing users have to do is to isolate the infected computer upon detection of the virus. This is to prevent the virus from spreading to other corporate computers causing more damage. Then, scan the computer for viruses or other threats using anti-virus software so as to remove infections. Next is to find the infected computers and quarantine them by disconnecting the cable of the individual workstations from the network. By doing this, it will keep the infection of the virus under control. Lastly ensure if there are no more traces of infection before connecting it to the other uninfected computers. If the method does not work, user will have to reformat hard disk and reinstall the operating system. Reinstalling operating system is faster than running anti-virus scans, and is guaranteed to remove any malware.

As corporate LAN is more prone to virus attacks as compared with a home personal computer, security needed will have to be more secured. Each office should have a description of the current common viral programs and hoaxes, or access to a common source of information such as intranet page. Whatever list that is used must be kept up to date and it is essential that each organization of any size assign a person to support the prepared lists of local virus contacts and information.

Security Improvement For LAN

As personal computers brought in from outside can be a possible source of virus infection, there are two solutions which may help to minimize and to avoid the infection from happening.

First solution would be using VLAN so as to quarantine the unidentified personal computers. The computers are then scanned according to the security policy and will be allowed to connect to the corporate LAN if tested okay. Second solution would be virus protection gateway. As the traditional anti-virus technologies are unable to detect the network viruses and prevent the mass infection within LAN network, network administrator will help to prevent infections, threats and defend the corporate network from the viruses. Infected personal computers will also be blocked from connecting to the corporate LAN.

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