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Monday, 19 September 2011

Types Of Viruses

Not all computer viruses behave, replicate, or infect the same way. 
There are several different categories of viruses and malware. Below 
I list and discuss some of the most common types of computer viruses.

Trojan Horse:

A trojan horse program has the appearance of having a useful and desired 
function. While it may advertise its activity after launching, this
information is not apparent to the user beforehand. Secretly the
program performs other, undesired functions. A Trojan Horse neither
replicates nor copies itself, but causes damage or compromises the
security of the computer. A Trojan Horse must be sent by someone or
carried by another program and may arrive in the form of a joke program 
or software of some sort. The malicious functionality of a Trojan Horse may
be anything undesirable for a computer user, including data destruction or compromising a system by providing a means for another computer to gain
access, thus bypassing normal access controls.


A worm is a program that makes and facilitates the distribution of copies
of itself; for example, from one disk drive to another, or by copying itself
using email or another transport mechanism. The worm may do damage 
and compromise the security of the computer. It may arrive via exploitation
of a system vulnerability or by clicking on an infected e-mail.

Bootsector Virus:

A virus which attaches itself to the first part of the hard disk that is 
read by the computer upon bootup. These are normally spread by 
floppy disks.

Macro Virus:

Macro viruses are viruses that use another application's macro 
programming language to distribute themselves. They infect 
documents such as MS Word or MS Excel and are typically spread 
to other similar documents.

Memory Resident Viruses:
Memory Resident Viruses reside in a computers volitale memory (RAM). 
They are initiated from a virus which runs on the computer and they
stay in memory after it's initiating program closes.

Rootkit Virus:
A rootkit virus is an undetectable virus which attempts to allow 
someone to gain control of a computer system. The term rootkit comes 
from the linux administrator root user. These viruses are usually installed
by trojans and are normally disguised as operating system files.

Polymorphic Viruses:
A polymorphic virus not only replicates itself by creating multiple files
of itself, but it also changes it's digital signature every time it replicates. 
This makes it difficult for less sophisticated antivirus software to detect.

Logic Bombs/Time Bombs:
These are viruses which are programmed to initiate at a specific date or 
when a specific event occurs. Some examples are a virus which deletes
your photos on Halloween, or a virus which deletes a database table if 
a certain employee gets fired.


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