But for one to get us down it has to actually get in past our defenses and then affect that first, all-important cell. If it doesn't, it can't replicate. We don't get sick. Even if you have virus-infected program on your machine, it can't do anything to you until the first time you run it. Having said that, it is important to remember viruses are out there.
Real viruses are incredibly colorful, although potentially devastating pieces of code.
They can do everything from trash your hard drive to create havoc with your screen. I speak from experience. In 1992, the computer I was using at college was afflicted by a virus. I downloaded a scanner and managed to clean things up, but had the particular bug my PC caught been a bit more vicious, I might have had to reinstall everything. Since that time, a virus scanner runs on my computer constantly.