How are trojan horse produced?

Computer system viruses are developed by people who desire to trigger harm to others, or who want to gain control over somebody else's computer system. The most basic way to produce a virus is to take some existing code and customize it slightly. This brand-new code can then be distributed to others, who may unsuspectingly run it on their own computer systems. When the infection is running, it can do anything its creator desires it to, consisting of deleting files, taking information, or sending spam. More advanced viruses can be very difficult to eliminate and find. my explanation