To create a virus, a user or attacker needs to create a code. In this code the attacker needs to express what type of virus, he/ or she wants to use. Once the attacker determines what type of virus is going to be used, then they must determine who they want to attack. Lastly, ask what type of data they want to gain from the attack. People write computer viruses. The person has to write the code, test it to make sure it spreads properly and then release it. A person also designs the virus's attack phase, whether it's a silly message or the destruction of a hard disk. .
There are at least four reasons why this is done. The first is the same psychology that drives vandals and arsonists. For some people, that seems to be a thrill. If that sort of person knows computer programming, then he or she may funnel energy into the creation of destructive viruses. Secondly the reason has to do with the thrill of watching things blow up. Some people have a fascination with things like explosions and car wrecks. Creating a virus is a somewhat like that, it creates a virtual bomb inside a computer, and the more computers that get infected; the more "fun" the explosion. The third reason involves bragging rights; some people enjoy the status it holds. Certain types of programmers see security holes that could be exploited, and are compelled to exploit the hole themselves before someone else beats them to it. The reason that drives many people on a day-to-day basis to commit crimes, get easy cash, obtain illegal money, a fast payout; the idea of easy money. Viruses can trick you into buying fake software, steal your personal information and use it to get to your money, or be sold on the digital equivalent of the black market. Powerful viruses are valuable and potentially lucrative tools.
Of course, most virus creators seem to miss the point that they cause real damage to real people