How are virus produced?

Virus are produced by people who wish to trigger harm to others, or who wish to acquire control over somebody else's computer system. The most basic way to produce an infection is to take some existing code and modify it a little. This brand-new code can then be distributed to others, who might unwittingly run it on their own computer systems. Once the virus is running, it can do anything its creator wants it to, including erasing files, stealing information, or sending out spam. More sophisticated viruses can be extremely tough to identify and remove. check my source