As the way people exchange electronic information changes, so does the nature of viruses. For example, the boot-sector virus, which was very reliant upon the DOS operating system, is on the decline as people move to Windows and Windows NT operating systems. New viruses are able to migrate from Windows 98 to Windows NT and back again. According to the Virus Bulletin, eight of the top 10 reported viruses in March 1999 were macro viruses. In February 1999, that figure was even higher, with eight of the top 10 accounting for 83.9 percent of all reported incidents.
Macro viruses can mutate or become corrupted.
A mutant macro virus is essentially a new virus with a different fingerprint, making it difficult to detect with existing fingerprints. In addition, macro viruses can also mate when they meet in the same document, creating a third macro virus that has elements of both parent viruses. This type of virus generally infects uninfected programs when they are executed with the virus in memory. The boot sector contains specific information relating to the formatting of the disk and the data stored there. It also contains a small program called the boot program that loads operating system files.