Why malware?
All malware is designed to gain control of your computer.
Early on the motivation was probably power and “to see if I can do it.” Today the motivation is primarily financial.
Today’s viruses are designed to carry out tasks like sending email spam or conducting coordinated denial of service attacks against target companies, or even countries. Most are organized into botnets, massive networks of coordinated zombie computers that can be directed remotely and secretly to carry out
As we know from the organic world, a virus that kills its host cannot replicate and spread. So successful viruses in the electronic world, which also depend upon self-replication, must also survive in order to spread. Reformatting the computer’s disk isn’t necessarily a good survival mechanism – since it can also kill off the virus itself. So the most effective virus today is the one that lurks silently without giving any overt evidence that it’s there. The longer it lives in situ the greater the benefit to its creator
Malware— It’s software that does bad stuff.

