Getting Put Through the Shredder

I got this nasty virus/adware file yesterday. I thought I was downloading a video codec for quick time, but I quickly found out it was more than I bargained for. It would not let me delete the downloaded file and MacAfee did squat. I wound up downloading a number of other tools to clean my registry before I could shred the codec file. Why do people do this sort of thing? Why do they create these files to screw with our computers? If it is to get us to buy a product its pretty unsound business procedure. If its just maliciousness they should be thrown into a roomfull of people with infected computers to defend themselves. I can honestly say I felt quite murderous. If I ever run into a person who does this sort of crap I am going to throw punches. No questions. No answers. Just fists flying until the rage subsides.