Microsoft have said that over 65,000 viruses exist . What they don't mention is that there are very few virus threats for other operating systems like Linux or Mac OS X. A list of Linux viruses from Wikipedia.org gives some indication, especially considering that most or all of those Linux viruses are extinct in the wild and are no longer a threat. If any readers could provide a list of Mac OS X viruses I would be interested in reading it. I believe that only one or two threats exist for Mac OS X.
McAfee has a great virus map that shows how many computers around the world have been infected with viruses.
 Source — This is a Flash video about the large number of viruses for Windows. This video may be outdated and the number of actual viruses may be higher.