Guest Author - Debbie Jacobsen

Anyone who uses a computer has undoubtedly heard the terms “computer virus”,
“worm”, and “Trojan”, and most use these terms interchangeably to describe a
virus. What you may not realize though, is that computer worms and Trojan horses
are not computer viruses at all.

While each of these three computer security threats shares some common
characteristics, there are some distinct differences between viruses, worms, and
Trojans that cause them to stand on their own as a category of malicious
software. The main similarity is that all are bad, and can potentially cause
you, your computer, or your network a great deal of harm.

Common Characteristics of Viruses, Worms, and Trojans

All computer viruses, worms, and Trojan horses are considered to be
“malware”, also commonly referred to as malicious software. Spyware and adware
also fall into the category of malware, as is any other type of software that is
designed to perform malicious and/or unwanted activity.

Viruses, worms, and Trojans have been around for awhile, and are often
packaged together (i.e. a virus that launches a worm when executed, a worm
that plants a Trojan, etc…). Because of their longstanding use as a means of
performing disruptive and destructive tasks, anti virus software developers
include protection against Trojans and worms in their antivirus applications.
Anti virus software (if updated regularly) will help protect you from all three dangers.

Differences Between Computer Viruses, Worms, and Trojan Horses

A Computer Virus is attached to a program or file, and is
designed to spread from one computer to another. It infects the computer it is
installed on, and is usually spreads when the infected file (usually an .exe
file) is shared with others via email, disk, USB drive, or CD. A virus has
to have human action in order to launch and deliver its “payload”. The file that
the virus is attached to cannot open itself; a user has to open it in order to
execute the virus. Viruses have many symptoms, depending on the intent. Computer
viruses can erase or corrupt files and applications, crash your system by making
so many copies of files that the hard drive fills up, or make a computer
inoperable by altering critical system files.

A Computer Worm is like a virus in that it is also attached to
a file, and the file has to be opened before infection can take place. Unlike a
virus, that is passed from computer to computer via user action (usually
unintentional); worms are designed to self-replicate and spread without any
effort on the user’s part. When you open a file that contains a worm, it starts
spreading through networks and emails immediately. The main purpose of a worm
attack is to bring down systems and networks by consuming great amounts of
bandwidth and memory. Worms are also used as a means for a remote attacker to
tunnel into your system. Many worms will replicate themselves by sending
“clones” to everyone in your email address book. These emails are sent out
immediately upon opening the infected file, and may not show up in your “sent
items” folder.

A Trojan Horse is also included in a file, and like a virus,
does not propagate itself. Trojans are tricky, in that they are often disguised
as some type of useful or interesting software. When the software is installed
(Trojans are normally embedded in .exe files), the Trojan is activated,
and sometimes you don’t even realize its there. Trojans can do many things, and
while some are designed to be dangerous, others are just annoying. A Trojan
might destroy certain types of files, alter critical system files, change your
desktop icons, or simply plant a “backdoor” on your system that can be used by a
hacker or cyber criminal at a later date. Trojans are usually passed from PC to
PC by email or disk file transfer, because the sender doesn’t know that the file
carries a harmful Trojan.

Protection from Viruses, Worms, and Trojans

The good news is that anti virus software will provide a great deal of
protection against known computer viruses as well as worms and Trojan horses.
The bad news is that antivirus software won’t necessarily provide total
protection. You still need a good firewall to keep cyber criminals out, and you
need anti spyware to protect against the other types of malware that antivirus
software isn’t so good at catching.

Once you have antivirus software, you must update it regularly (daily
updating is recommended). Most anti virus products include an auto-update
feature, which makes this a painless task.

Perform a total system scan as soon as you have installed and updated your
antivirus software, and then do the system scan again each week. Most products
allow you to schedule system scans (which can take some time on large hard
drives) for a time when you are not using your PC.

Be sure to get the most recent updates for your operating system and all
applications installed on your PC. This is especially important for Windows
users, as the majority of malware is designed to work on the world’s most
popular operating system. Updates will patch newly discovered “security holes”
and will help prevent many viruses, worms and Trojans from completing their
“mission”.