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Below is a general Virus Primer from
Trend Micro's web site.
Malware refers to a program that performs unexpected or unauthorized, but always malicious, actions. It is a general term used to refer to viruses, Trojans, and worms. Malware, depending on their type, may or may not include replicating and non-replicating malicious code. Due to the many facets of malicious code or a malicious program, referring to it as malware helps to avoid confusion. For example, a virus that also has Trojan-like capabilities may be called malware.
A computer virus is a program – a piece of executable code – that has the
unique ability to replicate. Like biological viruses, computer viruses can
spread quickly and are often difficult to eradicate. They can attach
themselves to just about any type of executable file and are spread as files
that are copied and sent from individual to individual.
In addition to replication, some computer viruses share another commonality:
a damage routine that delivers the virus payload. While payloads may only
display messages or images, they can also destroy files, reformat your hard
drive, or cause other damage. If the virus does not contain a damage
routine, it can cause trouble by consuming storage space and memory, and
degrading the overall performance of your computer.
A Trojan is a malware that performs a malicious action, but has no
replication abilities. Coined from Greek mythology's Trojan horse, a Trojan
may arrive as a seemingly harmless file or application, but actually has
some hidden malicious intent within its code.
Trojan malware usually have a payload. When a Trojan is executed, you may
experience unwanted system problems in operation, and sometimes loss of
valuable data.
A computer worm is a self-contained program (or set of programs) that is
able to spread functional copies of itself or its segments to other computer
systems. The propagation usually takes place via network connections or
email attachments.
More recent worms have also discovered ways to propagate using Instant
Messengers, via file sharing applications, and by collaborating with other
malware such as Trojans or other worm variants. WORM_BAGLE.BE, for example,
forms a vicious worm-Trojan cycle with TROJ_BAGLE.BE, in which the worm
mass-mails copies of the Trojan, and the Trojan downloads copies of the
worm. Additionally, the FATSO family is a family of worms that propagate via
an instant messaging application and a popular peer-to-peer file sharing
application.
Some worms may have an additional payload, such as preventing a user from
accessing antivirus Web sites, or stealing the licenses of installed games
and applications.
The life cycle of a malware begins when it is created and ends when it is
completely eradicated. The following outline describes each stage:
Creation Until recently, creating a malware required knowledge of a computer
programming language. Today anyone with basic programming knowledge, and
Internet access, can create a malware. Whole Web sites exist whose only
intent is to spread malicious code, and to encourage individuals to develop
their own harmful version of already existing, and tried-and-tested
malicious programs.
Replication and Propagation Malware propagate in a number of ways. Worms may
spread via email, instant messengers, or network shares. Viruses replicate
within a system, while some viruses also have automatic propagation
techniques similar to worms. Trojans. while not having any automatic form of
replication and propagation, are nevertheless available all over the
Internet, and the links to download them from may be included in email
messages, or other Web sites.
For more information on the propagation techniques of today's malware types,
read more here.
Activation Most malware perform their malicious activities upon execution.
Some have certain payloads that are activated only at a certain trigger
date, or with the onset of a specific trigger condition.
Discovery This phase does not always follow activation, but typically does.
When a malware is detected and isolated, it is sent to the ICSA in
Washington, D.C., to be documented and distributed to antivirus software
developers. However, with the rapid development of technology, and the ease
by which malware authors create their programs, most malware are released to
unsuspecting users even before they are discovered by the "authorities".
This is all the more reason to protect your system from the threats that
surround the computing world today.
Assimilation At this point, antivirus software developers modify their
software so that it can detect the new malware. This can take anywhere from
one day to six months, depending on the developer and the malware type.
Eradication If enough users install up-to-date virus protection software,
any malware can be wiped out. So far no malware have disappeared completely,
but some have long ceased to be a major threat.
What can you do to Protect against Malware?
There are many things you can do to protect against malware. At the top of
the list is using a powerful antivirus product, and keeping it up-to-date
with the latest pattern files.