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Q: What is a computer virus?
A: 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.
Q: What kind of files can spread
viruses?
A: 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. This includes
graphics and sound
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 computer
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.
Q: How do viruses spread?
A: 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
floppies.
Some viruses, known as 'multipartite' viruses, can spread both
by infecting
files and by infecting the boot areas of floppy disks.
Q: What do viruses do to
computers?
A: 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 virus
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. Warnings
about viruses that will physically destroy your computer are
usually hoaxes,
not legitimate virus warnings.
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