For example, the boot-sector virus 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. Macro Viruses . Whereas most viruses used to spread via floppy disks and program files, more infections occur now because of e-mail attachments and downloading from the Internet. According to the Virus Bulletin, eight of the top 10 reported viruses are macro viruses.
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. File Infectors . This type of virus generally infects uninfected programs when they are executed with the virus in memory. Boot Sector Infectors .