It's been six years since the Melissa macro virus first got loose, but security experts say network administrators and PC owners <A HREF="http://news.zdnet.com/2100-1009_22-5643900.html?tag=zdnn.alert">still have lessons to learn</A> from it. The virus started spreading on March 26, 1999, and traveled quickly across the Internet, using the macro functions in Microsoft Word to burrow into the computers of victims who opened the document. Within three days, hundreds of thousands of PCs were infected.