Why were viruses made?

Viruses weren't so much made as evolved from complex molecules, they are probably the simplest form of life. (in some cases they aren't even classified as alive)

Unless you're referring to computer virii, in which case they were originally written for fun, just do do funny stuff to computers, like pop up messages on the screen on April fools day, for example. Later on criminals and other wrong-doers decided that viruses were the perfect way to disrupt computer users, and in some cases exploit money from people.