A computer virus is a program that has no useful application, it has merely been developed to copy itself and infect computers and peripheral computer devices. Other dangerous software such as spyware and adware are not viruses as they cannot reproduce automatically. Many go unnoticed by the user as they perform their activities.

The first virus was developed as far back as the early 1970s. Since then, viruses have been developed extensively to infect systems running on commercial operating systems such as Microsoft Windows and Apple Mac OS. Sometimes the damage caused by a particular virus could be so high that the whole computer will have to be formatted. In this way, dangerous and more potent viruses such as Chernobyl have caused damage worth of millions of dollars by harming whole networks of computers.

Types of Viruses

Viruses have been categorized in to a number of groups based on their methods of propagation and what they do when they infect a computer. These types are:

•    Nonresident viruses – These viruses contain two main parts, the finder module and the replication module. The virus lies dormant in the computer as the finder module seeks out files that the virus can infect and the replication module infects those files with a copy of the virus.
•    Resident viruses – These have a replication module similar to nonresident viruses, however, they do not have a finder module. The virus loads itself on to the memory of the computer when the operating system performs some action, e.g. when a file is executed. Once the virus is loaded on to the memory, the replication module checks files to see whether they can be infected with the virus, and infects them with a copy of the virus.
•    Boot Sector viruses – This type of virus hides in the boot sector of storage disks and loads itself as the operating system whenever the boot sector is accessed.  When floppy disks were popular, this type of virus was used to infect a large number of computers by infecting the boot sectors of floppy disks which were used as boot disks. Nowadays boot sector viruses are rare.
•    Directory viruses – These viruses make a change to the directory structure of the computer. It moves original files to another location and replaces them with virus files with the same names as the original files. Whenever the user tries to execute the original files, they are actually executing the virus.
•    Macro viruses – These viruses infect macro-enabled applications such as Microsoft Word, Excel and Access. They can be run as macros and infect other documents once the document containing the macro virus is opened. Normally they do not harm the computer, but change text and images of documents in an annoying manner.
•    Polymorphic viruses – Polymorphic viruses encrypt themselves using a different algorithms and encryption keys every time they infect a system. This makes them harder to find for antivirus applications.
•    Companion viruses – These viruses accompany legitimate programs, and replicate themselves whenever the legitimate program is run. Therefore there will be virus files accompanying the files of the legitimate program in its folder.

The best way to avoid virus infections is to keep a frequently updated installation of a reputed antivirus software application installed on your computer. If you do not have such an installation and feel that your computer may have been infected with a virus, immediately use a web-based repair service or download a scanner of a reputed virus guard program and scan your computer. If all else fails, you may have to format your hard disk and reinstall your operating system to completely removed the virus.

In addition to security software you should also keep your web browser,operating system and applications like Java up to date.  This will help to ensure thatany security holes that have been fixed are applied to your computer.

Social Networking sites such as facebook, myspace, youtube, twitter are all great places to visit and connect with others.  Because of their popularity they also have criminals targetting them.  Be sure to avoid links from others that you do not trust.

E-mail: Many viruses are sent via e-mail.  To avoid scams and viruses you should not open up any attachments in e-mails or click on links in the e-mail unless you trust the sender.  Even if the e-mail is from a friend you should think twice about opening a link unless you trust the website they are sending you to.

When in doubt play it safe and always ensure your security software is up to date.


  1. Thanks very much for your youtube guide for removal of security shield 2011.
    After several replays of the clip I managed to get rid of the offending junk from my xp machine

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