The virus is a computer security software which belongs to the category of malware. Once executed it is capable of infecting files so that they reproduce by making copies of itself, usually without discovery by the user. From this point of view, the name is in perfect analogy with the virus in the biological field. Those who create these viruses are virus writers.
The virus may or may not be directly harmful to the host operating system, but even in the best case, however, it entails a waste of resources in terms of RAM, CPU and hard disk space.
As a general rule, it is assumed that a virus can directly damage the software of the machine that hosts it, although it can also indirectly cause damage to the hardware, for example, causing overheating of the CPU by overclocking, or by stopping the cooling fan. In common usage, the term virus is often and incorrectly used as a synonym of malware.
In 1949, John von Neumann proved mathematically the chance to build a computer program that can replicate autonomously. The concept of a self-replicating program found its practical evolution in the early 60s in the game devised by a group of programmers.
A virus is composed of a set of instructions, like any other computer program. It is usually composed of a very small number of instructions (from a few bytes to a few kilobytes).
It is specialized to run only a few simple operations and optimized for employing the fewest number of resources, so to be as invisible as possible. The main characteristic of a virus is to replicate and then spread into the computer each time you open the infected file. Anti Virus Support Sydney can detect and remove any infection.
However, a virus per se is not an executable program, just as a biological virus is not in itself a form of life. To be activated, a virus must infect a host program, or a sequence of code that is automatically launched, for example in the case of boot sector viruses.
The technique is usually used by viruses to infect executable files: the virus inserts a copy of itself into the executable file that must infect. The user sees the implementation of the program and does not realize that the virus is now running in memory and is taking various steps contained in its code as shown by Anti Virus Support Sydney.
Primarily, a virus makes copies of itself by spreading, but it can also have other much more harmful tasks (delete or destroy files, reformat your hard drive, open the backdoor to reveal messages, pictures or change the appearance of video).