Trojan Horse - a computer virus

Trojan Horse - a computer virus

The internet consists of hundreds of millions of computers distributed around the world. Millions of people use the internet daily, taking full advantage of the available services at both personal and professional levels. The internet connectivity among computers on which the World Wide Web relies, however renders its nodes on easy target for malicious
users who attempt to exhaust their resources or damage the data or create a havoc in the network. Computer Viruses, especially in recent years, have increased dramatically in number. One of the most highprofile threats to information integrity is the Computer Virus.

Surprisingly, PC viruses have been around for two-thirds of the IBM PC’s lifetime, appearing in 1986. With global computing on the rise, computer viruses have had more visibility in the past few years. In fact, the entertainment industry has helped by illustrating the effects of viruses in movies such as ”Independence Day”, ”The Net”, and ”Sneakers”. Along with computer viruses, computer worms are also increasing day by
day. So, there is a need to immunise the internet by creating awareness in the people about these in detail. In this paper I have explained the basic concepts of viruses and worms and how they spread.

A. Virus:
A self-replicating program. Some definitions also add the constraint saying that it has to attach itself to a host program to be able to replicate. Often Viruses require a host, and their goal is to infect other files so that the virus can live longer. Some viruses perform destructive actions although this is not necessarily the case.Many viruses attempt to hide from being discovered. A virus might rapidly infect every file on individual computer or slowly infect the documents on the computer, but it does not intentionally try to spread itself from that computer (infected computer) to other. In most cases, that’s where humans come in. We send e-mail document attachments, trade programs on diskettes, or copy files to file servers. When the next unsuspecting user receives the infected file or disk, they spread the virus to their computers, and so on.

B. Worms:
Worms are insiduos because they rely less (or not at all) upon human behaviour in order to spread themselves from one computer to others. The computer worm is a program that is designed to copy itself from one computer to another, leveraging some network medium: e-mail, TCP/IP, etc. The worm is more interested in infecting as many machines as possible on the network, and less interested in spreading many copies of itself on a single computer (like a computer virus). The prototypical worm infects (or causes its code to run on) target system only once; after the initial infection, the worm attempts to spread to other machines on the network. Some researchers define worms as a sub-type of Viruses. In early years the worms are considered as the problem of Mainframes only. But this has changed after the Internet become wide spread; worms quickly accustomed to windows and started to send themselves through network functions.
Some categories that come under worms are
_Mailers and Mass-Mailer worms

C. Trojan Horses:
A Trojan Horse is a one which pretend to be useful programs but do some unwanted action. Most Trojans activate when they are run and sometimes destroy the structure of the current drive (FATs, directories, etc.) obliterating themselves in the process. These does not require a host and does not replicate. A special type is the backdoor trojan, which does not do anything overtly destructive, but sets your computer open for remote control and unauthorised access.

D. Others:
There are other types of malicious programs apart from Viruses, Worms and Trojan Horses. Some of them are described below.

1) Logic Bombs:: A logic bomb is a programmed malfunction of a legitimate application. These are intentionally inserted in otherwise good code. They remains hidden with only their effects are being visible. These are not replicated. Bugs do everything except make more bugs.

2) Germs:: These are first-generation viruses in a form that the virus cannot generate to its usual infection process. When the virus is compiled for the first time, it exists in a special form and normally does not have a host program attached to it. Germs will not have the usual marks that the most viruses use in second-generation form to flag infected files to avoid reinfecting an already infected object.

3) Exploits:: Exploit is specific to single vulnerability or set of vulnerabilities. Its goal is to run a program (possibly remote, networked) system automatically or provide some other form of more highly previliged access to the target system.

The most common blunder people make when the topic of a computer virus arises is to refer to a worm or Trojan horse as a virus. While the words Trojan, worm and virus are often used interchangeably, they are not the same. Viruses, worms and Trojan Horses are all malicious programs that can cause damage to your computer, but there are differences among the three, and knowing those differences can help you to better protect your computer from their often damaging effects.
A computer virus attaches itself to a program or file so it can spread from one computer to another, leaving infections as it travels. Much like human viruses, computer viruses can range in severity: Some viruses cause only mildly annoying effects while others can damage your hardware, software or files. Almost all viruses are attached to an executable file, which means the virus may exist on your computer but it cannot infect your computer unless you run or open the malicious program. It is important to note that a virus cannot be spread without a human action, (such as running an infected program) to keep it going.  People continue the spread of a computer virus, mostly unknowingly, by sharing infecting files or sending e-mails with viruses as attachments in the e-mail.

A worm is similar to a virus by its design, and is considered to be a sub-class of a virus. Worms spread from computer to computer, but unlike a virus, it has the capability to travel without any help from a person. A worm takes advantage of file or information transport features on your system, which allows it to travel unaided. The biggest danger with a worm is its capability to replicate itself on your system, so rather than your computer sending out a single worm, it could send out hundreds or thousands of copies of itself, creating a huge devastating effect. One example would be for a worm to send a copy of itself to everyone listed in your e-mail address book. Then, the worm replicates and sends itself out to everyone listed in each of the receiver's address book, and the manifest continues on down the line. Due to the copying nature of a worm and its capability to travel across networks the end result in most cases is that the worm consumes too much system memory (or network bandwidth), causing Web servers, network servers and individual computers to stop responding. In more recent worm attacks such as the much-talked-about .Blaster Worm., the worm has been designed to tunnel into your system and allow malicious users to control your computer remotely.

A Trojan Horse is full of as much trickery as the mythological Trojan Horse it was named after. The Trojan Horse, at first glance will appear to be useful software but will actually do damage once installed or run on your computer.  Those on the receiving end of a Trojan Horse are usually tricked into opening them because they appear to be receiving legitimate software or files from a legitimate source.  When a Trojan is activated on your computer, the results can vary. Some Trojans are designed to be more annoying than malicious (like changing your desktop, adding silly active desktop icons) or they can cause serious damage by deleting files and destroying information on your system. Trojans are also known to create a backdoor on your computer that gives malicious users access to your system, possibly allowing confidential or personal information to be compromised. Unlike viruses and worms, Trojans do not reproduce by infecting other files nor do they self-replicate.
Added into the mix, we also have what is called a blended threat. A blended threat is a sophisticated attack that bundles some of the worst aspects of viruses, worms, Trojan horses and malicious code into one threat. Blended threats use server and Internet vulnerabilities to initiate, transmit and spread an attack. This combination of method and techniques means blended threats can spread quickly and cause widespread damage. Characteristics of blended threats include: causes harm, propagates by multiple methods, attacks from multiple points and exploits vulnerabilities.

To be considered a blended thread, the attack would normally serve to transport multiple attacks in one payload. For examplem it wouldn't just launch a DoS attack — it would also install a backdoor and damage a local system in one shot. Additionally, blended threats are designed to use multiple modes of transport. For example, a worm may travel through e-mail, but a single blended threat could use multiple routes such as e-mail, IRC and file-sharing sharing networks. The actual attack itself is also not limited to a specific act. For example, rather than a specific attack on predetermined .exe files, a blended thread could modify exe files, HTML files and registry keys at the same time — basically it can cause damage within several areas of your network at one time.

Blended threats are considered to be the worst risk to security since the inception of viruses, as most blended threats require no human intervention to propagate.

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