This virus is the first working Excel macro virus found in general circulation. This enables the infection of all other spreadsheets opened or created on the infected system in the future. CIH is a very destructive virus with a payload that destroys data. An infected system, therefore, must be rebooted from a clean system disk before scanning with an anti-virus product. W97M.Class , alias Class.
Most variants have a payload that displays messages on certain dates of the year.
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. 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 in March 1999 were macro viruses.