THE ANATOMY OF A VIRUS
A virus is a very small, simple organism that infects cells, known as the host, by attaching itself to them and using them to reproduce itself. This often causes harm to the cells.
Similarly, a virus is a very small program routine that infects a system and uses its resources to itself. It often does this by patching the system to enable it to detect files, such as COM or EXE files. It then copies itself into those files. This sometimes causes harm to the host computer system.
When the user an infected , it is loaded into memory carrying the virus. The virus uses a common technique to stay resident in memory. It can then use a routine to infect other programs. This process continues until the computer is switched .