What is a computer virus? Simply put, from wikipedia, A computer virus is a computer program that can copy itself and infect a computer.
I heard Leo LaPorte say that 84% of viruses come from hacked or bad websites... used to be that they almost exclusively came from email attachments.
Many people believe that once you have a virus it is time to throw your comptuer out... many people don't have the time or money to do that... many opt to have the computer cleaned. The biggest concern is that you may only think it is clean...
Why do we have viruses? There is a lot of money in it for one thing... many of these viruses will ask for a credit card to remove the malware from your computer... after you enter your credit card info nothing happens... you've just fed a bad guy your credit info. Some people send out viruses just to create problems.