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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 medium such as a floppy disk, CD, USB drive or by the
Internet. 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
computer
worms and
trojan horses. A
worm, however, can spread
itself to other computers without needing to be transferred as part of a
host. A
trojan horse is a file that appears harmless until executed. In contrast
to viruses,
trojan horses do not insert their code into other computer
files. 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. Furthermore, some sources use an alternative terminology in
which a virus is any form of self-replicating
malware.
The term comes from the term virus in biology. A computer virus
reproduces by making (possibly modified) copies of itself in the
computer's memory, storage, or over a network. This is similar to the
way a biological virus works.
Some viruses are programmed to damage the computer by damaging programs,
deleting files, or reformatting the hard disk. Others are not designed
to do any damage, but simply replicate themselves and perhaps make their
presence known by presenting text, video, or audio messages. Even these
benign viruses can create problems for the computer user. They typically
take up computer memory used by legitimate programs. As a result, they
often cause erratic behavior and can result in system crashes. In
addition, many viruses are bug-ridden, and these bugs may lead to system
crashes and data loss.
There are many viruses operating in the general Internet today, and new
ones are created and discovered every day.
Prevention and
Detection
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