What is a Computer Virus ?

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A computer virus is a malicious computer program that, when executed by an unsuspecting person, performs tasks that primarily include replicating itself and in some cases deploying a payload.

Over a decade or so ago, viruses were pretty straightforward. They got into a system and infected a file or two. It was as basic as ordering coffee when coffee was easy to order. “One coffee please black.”

Nowadays, the catalog of viruses you have to defend yourself against is frighteningly complex. In fact, it’s become as complex as, well, ordering coffee.

“Looks like you’ve been infected by a dropper that’s put a Trojan on your system, which deployed a multi-partite that opened a backdoor and also infected the master boot record.”


Sounds like an order at Starbucks, don’t you think?

These days a discussion about a virus can actually occur without using the word virus because sometimes viruses are worms or Trojan horses, which are virus-like nasties that act a little different than their infectious cousins.

Why are they called computer viruses? Well, because they have similar characteristics to biological viruses that infect humans in at least one way.

The computer variety jumps from computer to computer much like a cold virus jumps from your kids to you and from you to your spouse.

Don’t let all this frighten you, though. It’s not that hard to figure out and defend your computer against viruses is pretty straightforward. Still, if the idea makes you unsettled, skip ahead to the part of the chapter about how to easily protect yourself from viruses.

But I hope you stick around because the more you know, the geekier you will be. Okay, not really. But understanding them makes them much less scary.

Viruses were one of the first real security threats people had to deal with when personal computers started appearing in homes a couple of decades ago.

The first computer viruses were written in the 1980s; however, they really didn’t become a big threat until the late 1990s when everyone who owned a personal computer started connecting to the Internet.

Before then viruses spread via floppy disks or CDs. They would ride on the back of files stored on a disk or in the boot area of the floppy and replicate when the disk was inserted into the computer.

The Internet’s popularity has also turned into the chief reason that security on personal computers has become such a hot topic. A Net connection is an off-ramp from the Internet into your computer for all data. And guess what? For viruses, it’s a super highway.

some malware programs cause serious problems such as destroying the system files, causing disruption to the computer operation or gathering sensitive information while others may only have a light impact such as redirecting websites to pornographic content or annoying the users with pop-ups and banners.
In the normal routine, we have often seen every malicious program being referred to as a virus, but this is not correct! In fact, as mentioned earlier, there exist several malicious programs where the virus is one among them. Now, many of you may be wondering to know what’s the difference between them. Well, this article gives a detailed information on different types of malware that exist, how they work and how they differ from each other:

Computer Virus:

As we all know, this is the type of malware that has become highly popular and is one of the most widely discussed topics in the field of computer security. A virus is just a computer program that is designed to take unauthorized control of the infected computer so as to cause harm to the system’s data or degrade its performance.

Mode of operation:

Computer viruses operate by attaching themselves to an already existing file or program and replicates itself to spread from one computer to another. In most cases, they tend to infect executable files that are parts of legitimate programs. So, whenever the infected file is executed on a new computer, the virus gets activated and begins to operate by further replication or causing the intended damage to the system.
A virus cannot perform its task of harming and replication unless it is allowed to execute. This is the reason why viruses often choose an executable file as its host and get attached to them. Viruses are mainly classified into two types:
Non-Resident Viruses: This kind of virus will execute along with its host, perform the needful action of finding and infecting the other possible files and eventually transfers the control back to the main program (host). The operation of the virus will terminate along with that of its host.
Resident Viruses: In the case of resident viruses, whenever the infected program is run by the user, the virus gets activated, loads its replication module into the memory and then transfers the control back to the main program. In this case, the virus still remains active in the memory waiting for an opportunity to find and infect other files even after the main program (host) has been terminated.

Damages caused:

Viruses are known to cause the destruction of data and software programs. In some cases, a virus may do nothing other than just replicating itself. However, they are responsible for using a large portion of the system resources such as CPU and memory which results in the performance degradation of the computer.
In order to stay protected from a virus infection, you may refer my other post on 12 tips to maintain a virus free computer.

Trojan horse:

A Trojan horse or simply called as Trojan is a type of malicious program that disguises itself as something that is legitimate or useful. The main purpose of a trojan is to gain the trust of the user from the front end so that it gets the permission to be installed. But, from the back end, it is designed to grant unauthorized control of the computer to the hacker.

Mode of operation:

A Trojan horse does not depend on the host to carry out its operation. So, unlike a computer virus, it does not tend to attach itself to other files. Trojans are often disguised as video codecs, software cracks, keygens and other similar programs downloaded from untrusted sources. So, one has to be careful about those untrusted websites that offer free downloads.
One of the most popular examples is the DNSChanger trojan that was designed to hijack the DNS servers of the victimized computers. It was distributed by some of the rogue pornographic websites as a video codec needed to view online content.

Damages caused:

Trojan horses are known to cause a wide variety of damages such as stealing passwords and login details, electronic money theft, logging keystrokes, modify/delete files, monitor user activity etc.


Worms are standalone computer programs with a malicious intent that spread from one computer to another. Unlike viruses, worms have the ability to operate independently and hence do not attach themselves to another program.

Mode of operation:

Worms often use a computer network to spread itself by exploiting the security vulnerabilities that exist inside the individual computers. In most cases, worms are designed only to spread without causing any serious change to the computer system.

Damage caused:

Unlike viruses, worms do not cause damage to the system files and other important programs. However, they are responsible for consuming the bandwidth thereby degrading the performance of the network.


Spyware is a type of malicious software that can collect information about the activities of the target computer without the knowledge of its users. Spywares such as keyloggers are often installed by the owner or administrator of the computer in order to monitor the activities of the users. This can be a parent trying to monitor his child, a company owner trying to monitor his employee or someone trying to spy on his/her spouse.

Mode of operation:

Spywares are designed to operate in a total stealth mode so that its presence is completely hidden from the users of the computer. Once installed, they silently monitor all the activities on the computer such as keystrokes, web activity, IM logs etc. These logs are stored secretly for later access or uploaded online so that the installer of the spyware program can have access to them.

Damage caused:

Apart from monitoring, spyware does not cause any damage to the computer. However, in some cases, the affected computer may experience degradation in its performance.


Adware is a software program that automatically renders advertisements to the users without their consent. Most common examples are pop-ups, pop-unders, and other annoying banner ads. The prime reason behind the design of adware is to generate revenue for its author.

Mode of operation:

Adware is often bundled up with some of the free utilities such as browser toolbars, video downloaders etc. When such programs are installed, the adware may take over and distract user activity by displaying annoying advertisements.

Damage caused:

Adware is harmless in most of the occasions. However, some are known to contain spyware that is used to monitor the surfing habits of users. This may pose a threat to the privacy of the users.



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Micky World



One thought on “What is a Computer Virus ?

  1. It is very important not to download files or open emails from sources you are not familiar with. It pays to play it safe with suspicious emails and files.

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