How are virus created?

Bug are developed by people who wish to cause harm to others, or who want to get control over somebody else's computer. The simplest method to produce a virus is to take some existing code and modify it a little.  https://tourismcrisis.org/?p=381 This new code can then be dispersed to others, who might unknowingly run it on their own computer systems. Once the infection is running, it can do anything its creator wants it to, including erasing files, stealing data, or sending out spam. More sophisticated viruses can be extremely tough to eliminate and find.