A computer virus is a computer program that can copy itself[1] 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
Viruses, spyware, worms, trojans, adware… yikes! (1) Start taking steps to protect your private information...
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.