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What is a virus?
A computer virus is a small program written to alter the way a
computer operates, without the permission or knowledge of the user.
A virus must meet two criteria:
- It must execute itself. It will often place its own code
in the path of execution of another program.
- It must replicate itself. For example, it may replace other
executable files with a copy of the virus infected file. Viruses
can infect desktop computers and network servers alike.
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 to replicate themselves
and make their presence known by presenting text, video, and 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.
What is a worm?
Worms are programs that replicate themselves from system to system
without the use of a host file. This is in contrast to viruses,
which requires the spreading of an infected host file.
What is a Trojan Horse?
Trojan Horses are impostors--files that claim to be something desirable
but, in fact, are malicious. A very important distinction between
Trojan horse programs and true viruses is that they do not replicate
themselves. Trojans contain malicious code that when triggered
cause loss, or even theft, of data. For a Trojan horse to spread,
you must, invite these programs onto your computers--for example,
by opening an email attachment or downloading and running a file
from the Internet. The PWSteal.Trojan is a Trojan.
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