What is a computer virus?
A virus is a program that infects computer systems by attaching to other computer programs and/or boot sectors and/or partition sectors of hard and/or floppy disks where it may create copies of itself and may damage and/or corrupt and/or destroy data, and/or impact system performance.
The three most common versions of computer viruses are
1. File corruptors which attach themselves to program files and generally ‘hide’ themselves in memory the first time the ‘host’ program is run and then infect other programs when they are run.
These types of viruses usually infect .COM and .exe programs although some infect any program with executable code.
2. Macro Viruses are wtitten in scripting languages and infect packages which have a scripting language for example Microsoft Office (Word and Excel).
These viruses have been responsible for many of the past and recent virus infections mainly due to the vast numbers of files passed around by email systems.
3. Boot sector viruses infect system areas on disks and cause major problems as for example if a boot sector is infected with a virus every time you boot from this disk the virus becomes active in memory.
These viruses are difficult to remove as you have to remove them from the boot sector and the memory.
These are currently the most common types of virus but there are many other types of virus.