The word Malware is short for malicious software, and is a
general term used to describe all of the viruses, worms,
spyware, and pretty much anything that is specifically
designed to cause harm to your PC or steal your
information.
II. Viruses --> Wreak Havoc On Your Files
The term computer virus is often used interchangeably
with malware, though the two don’t actually have the
same meaning. In the strictest sense, a virus is a program
that copies itself and infects a PC, spreading from one file
to another, and then from one PC to another when the files
are copied or shared.
Most viruses attach themselves to executable files, but
some can target a master boot record, autorun scripts, MS
Office macros, or even in some cases, arbitrary files. Many
of these viruses, like CIH, are designed to render your PC
completely inoperable, while others simply delete or
corrupt your files—the general point is that a virus is
designed to cause havoc and break stuff.
You can protect yourself from viruses by making certain
your antivirus application is always updated with the
latest definitions and avoiding suspicious looking files
coming through email or otherwise. Pay special attention
to the filename—if the file is supposed to be an mp3, and
the name ends in .mp3.exe, you’re dealing with a virus.
III. Spyware --> Steals Your Information
Spyware is any software installed on your PC that collects
your information without your knowledge, and sends that
information back to the creator so they can use your
personal information in some nefarious way. This could
include keylogging to learn your passwords, watching your
searching habits, changing out your browser home and
search pages, adding obnoxious browser toolbars, or just
stealing your passwords and credit card numbers.
Since spyware is primarily meant to make money at your
expense, it doesn’t usually kill your PC—in fact, many
people have spyware running without even realizing it, but
generally those that have one spyware application
installed also have a dozen more. Once you’ve got that
many pieces of software spying on you, your PC is going
to become slow.
What many people don’t realize about spyware is that not
every antivirus software is designed to catch spyware. You
should check with the vendor to make sure the application
you are using to protect you from malware is actually
checking for spyware as well. If you come across a PC that
is already heavily infected, run a combination of
MalwareBytes and SuperAntiSpyware to clean it
thoroughly.
IV. Trojan Horses --> Install a Backdoor
Trojan horses are applications that look like they are doing
something innocuous, but secretly have malicious code
that does something else. In many cases, trojans will
create a backdoor that allows your PC to be remotely
controlled, either directly or as part of a botnet—a network
of computers also infected with a trojan or other malicious
software. The major difference between a virus and a trojan
is that trojans don’t replicate themselves—they must be
installed by an unwitting user.
Once your PC has been infected with the trojan, it can be
used for any number of nefarious purposes, like a denial of
service (DoS) attack against a web site, a proxy server for
concealing attacks, or even worse—for sending out
buckets of spam. Protection against trojans works the
same way as viruses—make sure that your antivirus
application is up to date, don’t open suspicious
attachments, and think long and hard before you try and
use a downloaded crack for Photoshop—that’s one of
malware authors’ favorite spots to hide a trojan.
V. Worms --> Infect Through the Network
Computer worms use the network to send copies of
themselves to other PCs, usually utilizing a security hole
to travel from one host to the next, often automatically
without user intervention. Because they can spread so
rapidly across a network, infecting every PC in their path,
they tend to be the most well-known type of malware,
although many users still mistakenly refer to them as
viruses.
Because worms often exploit a network vulnerability, they
are the one type of malware that can be partially prevented
by making sure your firewall is enabled and locked down.