Introduction:

A virus is a biological agent that reproduces inside the cells of living hosts. When infected by a virus, a host cell is forced to produce many thousands of identical copies of the original virus, at an extraordinary rate. Unlike most living things, viruses do not have cells that divide; new viruses are assembled in the infected host cell. But unlike still simpler infectious agents, viruses contain genes, which gives them the ability to mutate and evolve. Over 5,000 species of viruses have been discovered.

                                            

                                             fig:computer construction of virus particals

Types:

1. Resident viruses: These are permanent viruses dwelling in RAM memory. In this case, they would be in a position to overcome, as well as interrupt, all operations that the system executes. Their effects include corrupting programs and files that are closed, opened, renamed or copied.
2. Overwrite viruses: These viruses delete information that is in the infected files. In this case, the infected files would be rendered totally or partially useless. Unfortunately, you would only clean the infected file by deleting it completely, therefore losing original content.
3. Direct action viruses: This virus replicates itself, then acts when executed. Subject to satisfaction of particular conditions, the virus infects files located in the folders or computer directory. It is also in directories specified in the AUTOEXEC.BAT PATH. In most cases, it is located in hard drive’s root directory and takes particular action when the computer boots.
4. File infectors: This virus infects executable files or programs. On running the programs, the virus would be activated, then be able to carry out its damaging effects. Most of the existing viruses are in this category.