The original Wazzu virus consists of a single page of relatively simple code and was not encrypted. Because of this, everyone who caught the virus had a working copy of the virus source code to play with which accounts for the large number of variants of this virus. WM.NPAD - The NPAD macro virus also spreads rapidly. Most variants display text on the screen after some number of infections. They do no damage other than spread.
Macro viruses use the built-in Word.
Basic macro language available in Microsoft Word 6.0 and later. A variant of this language existed in Word 2.0 for Windows, but these macro viruses only run on the version of Word. Basic in Word 6.0 and later. Macintosh versions of Word earlier than 6.0 do not have a macro language though converters are available to allow Word 5 to read Word 6 files. Any Word 6 files converted to Word 5 will have all their macros removed during the conversion process and cannot be infected with a virus.