Overview Of Computer Viruses Computer Science Essay

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Virus is a software programming code that invaded into our computer operation system without our knowledge while downloading software, pictures, emails, etc. That runs against our wishes to gain access to our computer operation system, in most case, with bad intention. All computer viruses are man created and they can reproduce themselves. Even such a simple virus is dangerous because it will spread quickly on all available memory and put the system to a halt and it is perceived as a threat to both business and personnel information. An even more dangerous type of virus is one capable of transmitting itself across networks and bypassing security systems.

This assignment aim to explore in detail to management about various facts and issues about "three main viruses", their transmission and areas of infection, what specific viruses are and how to prevent from Viruses. Specifically, I will discuss at the details of LAN and its being infected through internet becomes manifold. In my analysis, I will also highlight the prevention LAN infected by virus.

Computer viruses are known to be a threat to both business and personal information systems. A virus is a self-spreading piece of software that runs as an executable program on a targeted system. It is not, however, a stand-alone piece of software. It must piggyback itself on something else, such as a piece of e-mail or other application program, and is "installed" on a victim machine when the user accesses the host software. Some virus infection can be relatively benign such as displaying a dialog box or it can be seriously destructive, deleting ¬les from a hard drive, causing a computer to reboot again and again, and so on. Some viruses are known to be polymorphic, meaning that they can change themselves as they propagate so that each copy looks a bit different from all others.

There are three ways of virus hides itself from detection:

Encrypts itself into cryptic symbols,

Alters the disk directory data to compensate the additional virus bytes and

Redirect disk data by using stealth algorithms.

Trigger events and direct attack are the common methods which cause a virus to explode on a targeted system. Most of the viruses operate in two phases:

Infection Phase: Virus writers usually decide when to infect the host system's programs. Some infections activate each time they are running and executed completely. Whereas some virus codes infect only when users trigger them which include a day, time, or a particular event.

Attack Phase: Viruses have normally triggered events to activate and corrupt systems but some bugged in the system then it replicates and performs activities like file deletion, increasing session time. They corrupt the targets only after spreading completely as intended by their writers.

Viruses Spreading and its Areas of Infection

Viruses are classified based on what they infect and how they infect. System Sector or Boot Virus are spread disk boot sectors and records. File Virus is spread executables in OS file system. Macro Virus infects documents, spreadsheets and databases such as Microsoft Word, Excel and Access. Source Code Virus is overwrites or appends host code by adding Trojan code in it. Network Virus is spread itself via email by using command and protocols of computer network.

There is a difference between general viruses and worms. A worm is a special type of virus that can replicate itself and use memory, but cannot attach itself to other programs. A worm spreads through the infected network automatically but a virus does not.

When virus attacks the systems, programs take longer to load than normal, computer's hard drive constantly runs out of free space, files have strange names which are not recognizable, programs act inconsistently and resources are used up easily. Virus damage can be grouped broadly under technical attributes where technicalities involved in the modelling and use of virus causes damage due to lack of control, difficulty in distinguishing the nature of attack, draining of resources, presence of bugs and compatibility problems.

Chapter (2)


In computers, viruses can be transmitted as an e-mail attachments, as downloads, or be present on a diskette or CD. The immediate source of them we have received is usually unaware that it contains a virus.

Three Main Classes of Viruses

File infectors: Some file infector viruses usually attach themselves to .com or .exe file types. But some can infect any types of file (.SYS, .OVL, .PRG, and .MNU) for which execution is requested. When infected program is loaded, the virus loaded along with it. Other file infector viruses arrive as wholly-contained programs or scripts sent as an attachment to an e-mail note. (Figure.1)

Figure.1 attaching .exe file to infect the programs

Source: www.microsoft.com

System or boot-record infectors. These viruses infect executable code found in certain system areas on a disk. They usually attach to the DOS boot sector on the Master Boot Record on hard disks. A typical scenario is to receive a CD ROM from an innocent source that contains a boot disk virus without knowing it. When our operating system is running, the files on the CD can be read without triggering the boot disk virus. However, if we leave the CD in the drive, and then turn the computer off or reload the operating system, the computer will look first in our CD ROM drive, find the CD with its boot disk virus, load it, and make it temporarily impossible to use our hard disk. This is why we should make sure we have a bootable external backup device.

Macro viruses. These are the most common viruses, but they are subject to do the least damage. Macro viruses infect our Microsoft Office application and typically insert unwanted formats and views.

Preventive measures against viruses

2.1.1 Anti-virus Software

As we know prevention is better than cure, it should not accept disks or programs without checking them first using a current version of an anti-virus software program and should turn off the internet connection when we are not using it. The best protection against a virus is to know the origin of each program or file loaded into the computer or open from e-mail program. Since this is difficult, we can use anti-virus software that can screen e-mail attachments and also check all of files regularly and remove any viruses that are found. And also, that software will give a warning message of new viruses. Unless the warning is from a recognized source, chances are good that the warning is a virus hoax. There are many anti-virus software vendors. Here is a list of some famous anti-virus software for personal use:

Kaspersky Anti-Virus

Norton Antivirus

ZoneAlram Extreme Security

AVG Free Edition


2.1.2 Proxy Firewall

A firewall is software that acts like a wall between computer and the Internet. Just like a real firewall keep fire from spreading from one area to another and tries to keep computer viruses from spreading form the Internet onto a computer or network. Most of large business organisations route their communications through a proxy server which is a component of firewall. Companies use firewalls to protect network resources from unauthorized personnel to sensitive company information such as payroll or personnel records. Even though some Operating Systems include personal firewalls, business users should purchase a hardware firewall. Because hardware firewalls stop intrusions before they break in the computer. And it screens all incoming and outgoing messages carefully by using a variety of screening techniques.

Chapter (3)


3.1 LAN

A Local Area Network (LAN) can connect computers and printers within a limited area such as an office. This LAN can link in with other LANs via wireless or network connectivity. Local Area Networks are widely used to share resources and exchange information by connecting personal computers and workstations. In a LAN, each workstation means individual computer has its own CPU with which it runs programs but it also able to access data and devices anywhere on the LAN. This means that many users can share same data information and expensive devices like laser printers. By sending e-mail or engaging in chat session users can also make use of LAN to interact with each other. So, if one computer is infected with viruses in the LAN, it could easily be spread to all workstations.

3.2 Internet Network and Attack

Information transmitted over networks has much higher security risks than it kept on the stand-alone computer. In a business, one of the important jobs of the network administrators is taking measures to protect a network form security risks. On the internet, the security risk is greater because if no central administrator is present. Every unprotected computer is easily attack by malware (malicious software) i.e. Viruses, Worms and Trojan horses, which are programs that act without a user's knowledge and deliberately alter the computer's operations. To determine if a network or computer is vulnerable to an internet or network attack or require assistance about Internet security breaches, the companies and individuals can contact or visit the Web site for the Computer Emergency Response Team Coordination Centre (CERT/CC) which is government funded Internet security research and development centre.

3.3 Treatments to LAN infected by virus

Proactive is better than reactive. Once a network or computer got infected by viruses, it will take times and money to recover back. All users in the network should know or educate the network and internet security. The network administrator should take following measure on the LAN.

Use updated anti-virus software.

Keep web browser and operating system up-to-date.

Scan all the e-mails before sending or receiving them.

Perform a virus scan at least once in a week.

Always scan the storage media before connecting it to your computer system.

However, if the network or computer still gets affected by virus even after following the above measures, then it will need to use advanced file recovery application to recover your lost data. These Partition Recovery tools ensure absolute recovery of all files and folders after almost all kinds of virus attacks.

Chapter (4)


Viruses come in different forms some are mere nuisances, others come with devastating consequences. Email worms are self replicating, and clog networks with unwanted traffic. Virus codes are not necessarily complex. It is necessary to scan the systems/networks for infections on a periodic basis for protection against viruses. Antidotes to new virus releases are promptly made available by security companies, and this forms the major countermeasure. For a new business installed a LAN desiring to connect the internet, first, it must be installed any suitable prevention method such as anti-virus software or firewall. Also, all users in the network should know or educate the network and internet security. Moreover, the jobs of the organizational network administrators to taking measures to protect a network form security risks is also important.