A computer network is a combination of computers and other computer related devices connected by communications channels for the purpose of sharing files and resources among the users. The network may be of many types, with unique features of its own.
The primary objective of computer network is to share the files among various users. Among the various networks of computers, the internet is definitely the most important inventions of modern age. It is a huge source of information on any topic, it brought the era of emails and point to point communication through voice and video, allowing anyone to communicate with anyone else in the world; and it is also a great medium of new kind of business - the online business. Everyone in the world today depend so much on the computer networks and specially the internet, that it has become a part of our daily life.

fig: Computer Networks

"I think computer viruses should count as life. I think it says something about human nature that the only form of life we have created so far is purely destructive. We've created life in our own image."
-Stephen Hawking.

A computer virus is only a program, similar to other computer programs. The only difference is that it is destructive. Stephen Hawking has said rightly that computer viruses should count as life. It clearly resembles the destructive aspect of human nature.

A computer virus is a computer program that can copy itself, and infect other computers. Other "destructive" computer programs like malware, spyware, adware, etc are also counted as viruses, but they are different, technically, from actual viruses. Many viruses have become famous in the past, by wreaking havoc in the field of computer industry. The viruses like Melissa virus in 1999, I Love You virus in 2000, Mydoom worm in 2004,Storm worm in 2007 etc have been famous for their destructive behavior.

What is a Virus?
A virus is a small piece of software that hides inside other software. For example, the virus may attach to a word document and spread itself to other files or programs when that document is accessed, and wreak havoc.






Types of virus

E-mail viruses
An E-mail virus travels through the e-mail messages, and replicates itself over by automatically mailing itself to the people in the victim's e-mail address book.

Trojan horses
A trojan horse is simply a computer program that claims to do one thing (it may claim to be a game) but instead does other things like damage some hardware or delete the files on the hard disk. They do not replicate automatically.

Worms
A worm is a small piece of software that uses computer networks and security holes to replicate itself. A copy of it scans the network for other security limits, and when it finds one, it copies itself to the new machine and starts replicating from that machine as well.


Computer viruses are so called because they share some of the traits of the biological virus. They pass from one computer to another, infecting each one, as the biological virus does. There are very few reasons for the existence of such virus. The first reason is the same psychology that drives the vandals and arsonists. Someone who likes to break a window on someone's house, paint signs (usually vulgar signs) on walls and buildings or burn down a beautiful forest seems to be a psychological thrill. Such persons enjoy doing damage. And computer virus is a very safe means of damaging other people's properties or whatsoever.

The second reason builds up from the pleasure of watching things blow up. Most people enjoy watching skyrockets. They are also fascinated with things like explosions and car wrecks, the reason why most movies nowadays have such scenes. Creating a computer virus is similar to that, and its a little different kind of explosion that more people would love to watch.

The next reason involves bragging rights, or the thrill of doing it. If one finds a new thing, like a big ancient tree that no one else has ever seen, he can "tell" about the tree to other people, or he can "show" them, to be the first to discover that tree. The computer virus is a means of showing that security hole in the computer system that no one else has detected before.

Recovery from viruses

Anti-virus software

An anti-virus software, as the name implies, works against the viruses - it helps to prevent the infection of the computer from the viruses, and if the computer is already infected, it helps to heal the computer by removing the virus, or in some cases, removing the infected file itself.
An anti-virus works mainly in two ways. The first and the most common method of detecting the virus is using a list of virus signature definitions. This works by comparing the contents of the computer's memory (RAM and boot sectors), and the files stored on fixed or removable drives against the database of known "virus signatures".

The second method is using heuristic algorithm to detect the viruses on the basis of the common behaviors that most of the viruses exhibit.

System restore

The system restore is a built-in feature of all windows family. It restores the registry settings and other critical system files and settings to a previous pre-set checkpoint. The checkpoint may be created by the system itself, during installation of hardwares and softwares, or it may be created manually by the user. But the defect of this method is that the files to restore the system are also saved on the hard disk itself, which may as well be infected by the virus.

Operating system re-install

Re-installing the operating system itself is another efficient method of virus removal, because while doing so, all the previous files stored on the hard disk on the partition where the operating system was, are deleted. But care must be taken in re-installing the operating system, because the new OS installation files may already be infected with viruses, and in addition to the system partition, other partitions of the hard disk may also be infected with the virus.