AHHH! Viruses...Yuck

Can any type of virus be good? You can get the flu virus, a cold virus...but yesterday.... I got a computer virus.....totally screwed up my computer! 24 hrs later and I am still trying to fix the problem....What I don't understand is why people create viruses to begin with...are people really that cruel? Do they really hate society enough to punish people who have done nothing to them?
Yes I am upset.... My final for my computer class is on my computer and I don't want to spend another 5 hrs creating another presentation. AHHH!