The most common reason viruses are created is to "correct" an issue. 85% of viruses do not make it into general population. of the 15% of the "viruses" that make into general pop are done for one of two reasons 1. popularity 2. make money (if I create something that company 123 cant stop you can sell it for a price). this is how car alarms came into existence . hehe

If viruses concern you alot than for a few things that will help

1. dont do something your not suppose to
2. be aware of what you are doing (most issues can be prevented by knowing what you are clicking on.
3. dont use IE - use mozilla
4. dont use windows - Vista Ultimate is somewhere around 400 dollars - Fedora Core, Ubuntu, etc = free

now these are just opinions so please respect them as that for the reason the world turns is that someone else has an opinion that is respected