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A
virus is a type of program that can replicate
itself by making (possibly modified) copies
of itself. The main criterium for classifying
a piece of executable code as a virus is
that it spreads itself by means of 'hosts'.
A virus can only spread from one computer
to another when its host is taken to the
uninfected computer, for instance by a user
sending it over a network or carrying it
on a removable disk. Additionally, viruses
can spread to other computers by infecting
files on a network file system or a file
system that is accessed by another computer.
Viruses are sometimes confused with worms.
A worm, however, can spread itself to other
computers without needing to be transferred
as part of a host. Many personal computers
are now connected to the Internet and to
local-area networks, facilitating their
spread. Today's viruses may also take advantage
of network services such as the World Wide
Web, e-mail, and file sharing systems to
spread, blurring the line between viruses
and worms.
Viruses
can infect different types of hosts. The
most common targets are executable files
that contain application software or parts
of the operating system. Viruses have also
infected the executable boot sectors of
floppy disks, script files of application
programs, and documents that can contain
macro scripts. Additionally, viruses can
infect files in other ways than simply inserting
a copy of their code into the code of the
host program. For example, a virus can overwrite
its host with the virus code, or it can
use a trick to ensure that the virus program
is executed when the user wants to execute
the (unmodified) host program. Viruses have
existed for many different operating systems,
including MS-DOS, AmigaDOS, and Mac OS;
today, the majority of viruses run on Microsoft
Windows.
A
legitimate application program that can
copy itself as a side-effect of its normal
function (e.g. backup software) is not considered
a virus. Some programs that were apparently
intended as viruses cannot reliably self-replicate,
because the infection routine contain bugs.
For example, a buggy virus can insert copies
of itself into host programs, but these
copies never get executed and are thus unable
to spread the virus. Self-replicating programs
that have very limited spreading capabilities
because of bugs are sometimes not considered
as being viruses.
Additional
Definitions:
Adware
Browser
Hijacker
Browser Plugin
Dialer
Malware
Scumware
Spyware
Theifware
Trojan Horse
Computer Virus
Worm
This
article is licensed under the GFDL.
It uses material from the Wikipedia
article "computer virus"
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