In fact some virus warnings have been circulating literally for years despite the best efforts of system administrators to stamp them out. They tend to flare up from time to time and then die down again, only to reappear later, and they are of sociological rather than computational interest. You can find further information about the phenomenon on the CIAC Internet Hoaxes page or the Computer Virus Myths page . No virus can do anything until it is executed. The Melissa virus is an example.
Protection is relatively simple.
You just have to tell Word not to automatically execute macros from documents, at least not without asking first. How you achieve this depends on your version of Word. Word 7a and Word97 can do it themselves. Autoexecution is inherently dangerous. Since there are currently 500 or so macro viruses around, and they aren't hard to create, this is somewhat error-prone.