I'm writing this in early May 1999. And some of those people have lost data they will never be able to replace. But a lot of people didn't have a-v software, and many of those who did have it didn't use it regularly or keep it updated. So a lot of people lost time, money, and irreplaceable data when the CIH virus activated simply because they didn't take basic precautions to protect themselves. A computer virus is a program designed to spread itself by first infecting executable files or the system areas of hard and floppy disks and then making copies of itself.
Viruses usually operate without the knowledge or desire of the computer user.
Viruses have the potential to infect any type of executable code, not just the files that are commonly called 'program files'. For example, some viruses infect executable code in the boot sector of floppy disks or in system areas of hard drives. Another type of virus, known as a 'macro' virus, can infect word processing and spreadsheet documents that use macros. And it's possible for HTML documents containing JavaScript or other types of executable code to spread viruses or other malicious code. Since virus code must be executed to have any effect, files that the computer treats as pure data are safe.