A computer virus is a computer program that can copy itself and infect a computer. The term “virus” is also commonly but erroneously used to refer to other types of malware, including but not limited to adware and spyware programs that do not have the reproductive ability. A true virus can spread from one computer to another
Here is a question for you: Did you create a recovery disk set as you were prompted to do when you got your computer? If you did, congratulations, you are computer savvy. If you didn’t, be grateful that the factory settings, which include the operating system, are hidden in a protected section of the hard disk that you cannot delete. I needed these settings to fix a friend’s computer that could no longer connect to the internet, wired or wireless. Why?
There is no point in repeating definitions of viruses and other malware here. I’ve taken a paragraph from wikipedia.org that explains about what nastiness can infect your computer. And I would definitely recommend that you take the time to read what Microsoft has to say on the subject.