computer security, computer virus is a self-replicating computer program
that spreads by inserting copies of itself into other executable code or
documents. A computer virus behaves in a way similar to a biological
virus, which spreads by inserting itself into living cells. Extending the
analogy, the insertion of a virus into the program is termed as an
"infection", and the infected file, or executable code that is not part of
a file, is called a "host". Viruses are one of the several types of
malicious software or malware. In common parlance, the term virus is often
extended to refer to worms, trojan horses and other sorts of malware;
viruses in the narrow sense of the word are less common than they used to
be, compared to other forms of malware. However, in a stricter sense,
viruses, worms and Trojans are different from one another. They have
different characteristics and behaviors.
While viruses can be intentionally destructive, for example, by destroying
data, many other viruses are benign or merely annoying. Some viruses have
a delayed payload, which is sometimes called a bomb. For example, a virus
might display a message on a specific day or wait until it has infected a
certain number of hosts. A time bomb occurs during a particular date or
time, and a logic bomb occurs when the user of a computer takes an action
that triggers the bomb. The predominant negative effect of viruses is
their uncontrolled self-reproduction, which wastes or overwhelms computer
Today, viruses are somewhat less common than network-borne worms, due to
the popularity of the Internet. Anti-virus software, originally designed
to protect computers from viruses, has in turn expanded to cover worms and
other threats such as spyware, identity theft and adware.
Computer for Viruses using Online Virus Scanning Services
in the many types of viruses are:
A Trojan horse is just a computer program. The program pretends to do one
thing (like claim to be a picture) but actually does damage when one
starts it (it can completely erase one's files). Trojan horses cannot
A worm is a piece of software that uses computer networks and security
flaws to create copies of itself. A copy of the worm will scan the network
for any other machine that has a specific security flaw. It replicates
itself to the new machine using the security flaw, and then begins
scanning and replicating anew.
An e-mail virus will use an e-mail message as a mode of transport, and
usually will copy itself by automatically mailing itself to hundreds of
people in the victim's address book.
Logic bombs maliciously cause legitimate applications to fail. "An
application, for example, might delete itself, along with all information
and files from the disk, after a couple of runs as a copy protection
scheme. The logic bombs may transfer itself to other applications and
storage items, i.e. floppy disks, CD-ROM disks, and CD Disks."
A computer virus will pass from one computer to another like a real
life biological virus passes from person to person. For example, it is
estimated by experts that the Mydoom worm infected a quarter-million
computers in a single day in January of 2004. In March of 1999, the
Melissa virus spread so rapidly that it forced Microsoft and a number of
other very large companies to completely turn off their e-mail systems
until the virus could be dealt with. Another example is the ILOVEYOU
virus, which occurred in 2000 and had a similarly disastrous effect.
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
Trojan Horses are imposters--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. Trojan.Vundo is a
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. Although worms generally
exist inside of other files, often Word or Excel documents, there is a
difference between how worms and viruses use the host file. Usually the
worm will release a document that already has the "worm" macro inside the
document. The entire document will travel from computer to computer, so
the entire document should be considered the worm W32.Mydoom.AX@mm is an
example of a worm.
Use anti-virus software
Install anti-virus software on your computer, and ensure that it is kept
up to date. Because new viruses can spread extremely quickly, it is
important to update the virus pattern files on a regular basis. Old
anti-virus software will probably do little to protect you from new
Use an email filtering
Since most viruses are spread through email, it is important to
use an email system that scan inbound and outbound email and blocks
viruses. Most popular antivirus software does this however find out
if your service provider blocks viruses at the email server level.
Some service providers charge a fee for this but in the end, it is worth
the extra cost.
Use a firewall to protect your computer or computer network from the
internet. Computers connected to the outside world, such as those
connected directly to a DSL modem, a cable modem, or a dialup connection,
should be properly protected from internet threats via a firewall.
The firewall can be either a piece of hardware separating your computer or
network from the outside world, or the firewall can be a software type
firewall, such as the firewall built into Windows XP.
up-to-date with software patches
Many software vendors issue advisories on security issues. Turn on
Automatic Updates in Windows and install updates.
Back up your data regularly
Make regular backups of important data and files like pictures and
documents. If backing up to tape drives, CDs or DVDs, check that the
backups were successful. You should also find a safe place to store your
back-ups, perhaps even off-site in case of fire.
Common Causes of a slow PC
So what causes a PC to run
slow? There are many causes. Read about some of the most common here.
Editing the Registry
The Registry is a database of nearly all the settings for Windows
operating system and most of your installed applications. Learn how to
edit and clean it yourself.
Unless you know how to avoid it
and/or combat it, you probably have it on your computer.
Learn about viruses and find out how
to scan and remove them for Free.
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