A computer virus is a malicious program that can be made by people who wish to cause damage or disruption to systems and computers. They are coded bits that are attached to other programs or applications and when activated, spread like wildfire. Typically, viruses can be discovered attached to a file or program that is downloaded from the internet or shared via email. Many countries consider it to be illegal to develop and spread computer viruses.
In the world of computer viruses, there are a variety of different types that can infect machines in different ways. Some depend on a program to begin their work however, others are completely independent and are able to attack multiple systems without the need for the host. Computer viruses that utilize host programs to infect computers are often called worms, but those that do not employ this method of infection via other programs are referred to as viruses.
Certain viruses may begin to infect a system as soon as they arrive, whereas others remain undetected until the user unwittingly executes the code. The first computer virus was developed in 1974, and it performed as a biological virus by rapidly multiplying itself and causing harm to the system. Stuxnet is an example of an extremely destructive computer virus. It was created to destroy computerized centrifuges that were used to enrich Uranium.
It is not for the weak-hearted to try this task. However it is a fun and fascinating way to test your proficiency in computer programming languages and systems. There are many resources that will show you how to create a virus, if you are willing and able to put into the effort.