A Macro Virus refers to a serious type of malware that affects Microsoft Word and Excel. These viruses spread among Word and Excel applications and documents, and, unlike other types of malware, affect both Macs and Windows.
Some programs let users create "macro" commands, using both menu commands and a programming language to create routines to save time and perform complex tasks. Microsoft Word and Excel are the two most common such programs, and macro viruses, which use the Visual Basic language that these programs work with, are very common. They can damage Word or Excel files, and render these applications unusable. In addition, they are cross-platform: many macro viruses affect Windows and Mac OS X alike.