What is Computer viruse

Computer Viruses

The term virus covers a wide range of computer programs that have one thing in common. Once released, they replicate in a way that cannot be controlled by their author. This can easily, intentionally or unintentionally, lead to worldwide epidemics where millions of computers may become infected. The virus problem has increased in importance over the past ten years. The first viruses were merely an annoyance that did not cause much harm for any business.

The name virus is borrowed from biological science. A biological virus is a passive element that floats around until it hits a suitable cell. The mechanisms of the matching cell are then used to reproduce the biological virus, to express it in a simplified way. The term virus is rather suitable for computer-based equivalents, as computer viruses are passive in the same way. They attach to a carrier object and wait for the object to be transmitted to another computer. Once transmitted,

they activate and start looking for other objects to infect.

How does a virus spread?

A virus is by definition a computer program that spreads or replicates by copying

itself.However, the ability to replicate itself is the commoncriterion that distinguishes a virus from other kinds of software.The term virus is quite often misused. Some viruses contain routines that damagethe computer system on which it runs. This so called payload routine may alsodisplay graphics, play sounds or music etc. This has lead to a situation whereviruses are assumed to cause deliberate damage, even if there are many virusesthat don’t. The term virus has, for these reasons, become a synonym for malicioussoftware, which is incorrect from a technical point of view.

 

The process of spreading a virus includes both technical features in the virus itselfand the behavior of the computer user. Most viruses are by nature parasitic. Thismeans that they work by attaching themselves to a carrier object. Thisobject may be a file or some other entity that is likely to be transmittedto another computer. The virus is linked to the host object in such a

way that it activates when the host object is used. Once activated, the virus looks for other suitable carrier objects and attaches itself to them. This dependency on the human factor

slows down the replication of viruses.

(Another closely related program type, a worm, reduces this dependency and is able to replicate much faster.)

From this we can draw the conclusion that a virus does not appear as an object in itself. A virus always resides hidden in some useful object. A macro (File) virus may, for example, infect an important document, but the user does not notice this as the document looks perfectly normal and may be used just like any other document. This means that it is hard for an ordinary user to tell if a system is or is not infected. Special software is needed to examine the system and detect a virus

infection.

Understanding the structure of virus