If you do not want a computer virus... try downloading and using the LINUX OS. I never had a problem with it. When I had it, it wasnt as compatible with other things I wanted to use but is becoming increasingly popular all the time.
Apple equipment will not easily catch viruses for it has different operating system from other computers. But it is also highly advised to take care when surfing on the Internet. In addition, if your computer is accidentally affected, don't worry, many company like http://blog.doofix.com/ specializing in computer problems will help you completely remove the virus.