A computer virus is a program designed to spread itself by
executable files or the system areas of hard and floppy disks and then
making copies of itself. Viruses usually operate without the knowledge
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
types of executable code to spread viruses or other malicious code.
Since virus code must be executed to have any effect, files
computer treats as pure data are safe. This includes graphics and
files such as .gif, .jpg, .mp3, .wav, etc., as well as plain text in .txt
files. For example, just viewing picture files won't infect your
with a virus. The virus code has to be in a form, such as an .exe program
file or a Word .doc file, that the computer will actually try to execute
When you execute program code that's infected by a virus, the virus code
will also run and try to infect other programs, either on the same computer
or on other computers connected to it over a network . And the newly
infected programs will try to infect yet more programs.
When you share a copy of an infected file with other computer users,
running the file may also infect their computers; and files from those
computers may spread the infection to yet more computers.
If your computer is infected with a boot sector virus, the virus tries to
write copies of itself to the system areas of floppy disks and hard disks.
Then the infected floppy disks may infect other computers that boot from
them, and the virus copy on the hard disk will try to infect still more
Some viruses, known as 'multipartite' viruses, can spread both by infecting
files and by infecting the boot areas of floppy disks.
Viruses are software programs, and they can do the same things as any other
programs running on a computer. The actual effect of any particular
depends on how it was programmed by the person who wrote the virus.
Some viruses are deliberately designed to damage files or otherwise
interfere with your computer's operation, while others don't do anything but
try to spread themselves around. But even the ones that just spread
themselves are harmful, since they damage files and may cause other problems
in the process of spreading.
Note that viruses can't do any damage to hardware: they
won't melt down your
CPU, burn out your hard drive, cause your monitor to explode, etc.
about viruses that will physically destroy your computer are usually hoaxes,
not legitimate virus warnings.