Computer Virus


Virus is a computer program that can copy itself and infect a computer without the permission or knowledge of the owner.

a software program capable of reproducing itself and usually capable of causing great harm to files or other programs on the same…

A computer virus is a program or piece of code that is loaded onto your computer without your knowledge and runs against your wishes. Viruses can also replicate themselves. All computer viruses are man-made. A simple virus that can make a copy of itself over and over again is relatively easy to produce. Even such a simple virus is dangerous because it will quickly use all available memory and bring the system to a halt. An even more dangerous type of virus is one capable of transmitting itself across networks and bypassing security systems.


 Types of viruses

 Trojan Horses

A Trojan Horse program has the appearance of having a useful and desired function.

A Trojan Horse neither replicates nor copies itself, but causes damage or compromises the security of the computer.

A Trojan Horse must be sent by someone or carried by another program and may arrive in the form of a joke program or software of some sort

appears as interesting program file but when installed it allows intruders to access and read your files



A computer worm is a self-replicating computer program.

It uses a network to send copies of itself to other nodes (computers on the network) and it may do so without any user intervention.

It does not need to attach itself to an existing program.

virus that copies and multiplies itself by using computer networks and security flaws


Logic Bombs

Their objective is to destroy data on the computer once certain conditions have been met.

These are viruses which are programmed to initiate at a specific date or when a specific event occurs.

Some examples are a virus which deletes your photos on Halloween, or a virus which deletes a database table if a certain employee gets fired.


E-mail Viruses

use e-mail messages to spread which allow it to automatically forward itself to thousands of people


Boot Sector Virus

This type of virus affects the boot sector of a floppy or hard disk.

This is a crucial part of a disk, in which information on the disk itself is stored together with a program that makes it possible to boot (start) the computer from the disk.

These are normally spread by floppy disks.

Infects the boot or MBR of diskettes and hard drives through the sharing of infected disks and pirated software applications

Once your hard drive is infected all diskettes that you use in your computer will be infected


Program Virus

Becomes active when the program file (usually with extensions .BIN, .COM, .EXE, .OVL, .DRV) carrying the virus is opened

It then makes copies of itself and will infect other programs on the computer


Multipartite Virus

Hybrid of a Boot Sector and Program viruses It infects program files and when the infected program is active it will affect the boot record


Stealth Virus

Disguises itself to prevent from being detected by antivirus software

It alters its file size or conceals itself in memory


Polymorphic Virus

Act like a chameleon, changing its virus signature (binary pattern) every time it multiples and infects a new file


Macro Virus

Macro viruses are viruses that use another application’s macro programming language to distribute themselves.

They infect documents such as MS Word or MS Excel and are typically spread to other similar documents.

Programmed as a macro embedded in a document, usually found in Microsoft Word and Excel

Once it gets in to your computer, every document you produce will become infected

Relatively new type of virus and may slip by your antivirus software if you don’t have the most recent version installed


Directory Virus

Directory viruses change the paths that indicate the location of a file.


Resident Virus

This type of virus is a permanent which dwells in the RAM memory.

From there it can overcome and interrupt all of the operations executed by the system: corrupting files and programs that are opened, closed, copied, renamed etc.

Anti- Virus

Antivirus Software

“antivirus” is protective software designed to defend your computer against malicious software. Malicious software, or “malware” includes: viruses, Trojans, keyloggers, hijackers, dialers, and other code that vandalizes or steals your computer contents. In order to be an effective defense, your antivirus software needs to run in the background at all times, and should be kept updated so it recognizes new versions of malicious software.

Antivirus Software is used to prevent, detect, and remove computer viruses, worms, and Trojan horses.


 Antivirus basic functions:

– Scan your storage media

– Remove

– Heal / Repair

– Quarantine

– Update virus definitions

Examples of Antivirus Software

• Norton Antivirus


• Kaspersky

• Avast!

• PC-Cilin

• McAffee






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