A Trojan is not a computer virus in the sense that it doesn't get into
your system and self-replicate. The Trojan derives its name from
the ancient Greek story of the Trojan Horse, where a group of
warriors invades a city by hiding within a giant wooden horse. The
residents of the city thought the horse to be a gift, never knowing
what was hidden inside, so they rolled the horse in bringing their
enemy within the city walls with it. The Greek Trojan horse
appeared to be something that it was not, just as the computer
Trojan is. A computer Trojan is software that appears to function in
a certain way, when in reality it performs another action. A Trojan is
not always harmful and damaging to your system, but it can open a
back door for hackers to get into your computer and cause damage
or retrieve information.It is a program which does an unauthorized
function, hidden inside an authorized program. It does something other
than what it claims to do, usually something malicious
and it is intended by the author to do whatever it does. If it's not
intentional, its called a 'bug' or, in some cases, a feature :) Some
virus scanning programs detect some trojans. Some virus scanning
programs don't detect any trojans. No virus scanners detect all
Trojans.
Virus:
Computer Viruses have been around since the early 1980's.
A virus is an independent program which reproduces itself. It may
attach to other programs, it may create copies of itself (as in
companion viruses). It may damage or corrupt data, change data, or
degrade the performance of your system by utilizing resources such as
memory or disk space. Some virus scanners detect some viruses. No
virus scanners detect all viruses. No virus scanner can protect
against "any and all viruses, known and unknown, now and forevermore".
Because every anti virus updates their database after the virus come to
existence.
Worm:
Made famous by Robert Morris, Jr. , worms are programs which reproduce
by copying themselves over and over, system to system, using up
resources and sometimes slowing down the systems.
Computer Worms are like a virus in the fact that they do self-replicate
themselves within your computer system. However, a computer worm
does not have to attach itself to a program in your system like a computer
virus does in order to function. Also, unlike a computer virus that generally corrupts
and modifies files on your computer to cause damage, a computer worm
generally localizes its damage to the computer network. Computer worms
can often spread via email such as the SoBig and MyDoom worms did
(from 2003 and 2004 respectively).They are self contained and use the networks
to spread, in much the same way viruses use files to spread.
Spyware:
software that covertly gathers user information through the user's Internet
connection without his or her knowledge, usually for advertising purposes.
Spyware applications are typically bundled as a hidden component of freeware
or shareware programs that can be downloaded from the Internet; however, it should
be noted that the majority of shareware and freeware applications do not come with
spyware. Once installed, the spyware monitors user activity on the Internet and
transmits that information in the background to someone else. Spyware can also
gather information about e-mail addresses and even passwords and credit card numbers.
Aside from the questions of ethics and privacy, spyware steals from the user by using
the computer's memory resources and also by eating bandwidth as it sends information
back to the spyware's home base via the user's Internet connection. Because spyware
is using memory and system resources, the applications running in the background can
lead to system crashes or general system instability.Because spyware exists as
independent executable programs, they have the ability to monitor keystrokes, scan
files on the hard drive, snoop other applications, such as chat programs or word
processors, install other spyware programs, read cookies, change the default home
page on the Web browser, consistently relaying this information back to the spyware
author who will either use it for advertising/marketing purposes or sell the information
to another party.
Logic Bomb:
Code which will trigger a particular form of 'attack' when a
designated condition is met. For instance, a logic bomb could delete
all files on Dec. 5th. Unlike a virus, a logic bomb does not make
copies of itself.
While different in the functions they perform, Viruses, Trojans, Worms and
Spyware are all damaging to your computer. It is most important
you have proper computer protection software in place
that will protect you from these things so they cannot get into your computer
and cause damage.
