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Computer viruses What are they, what types are there and which are the most famous and dangerous?

Computer viruses What are they

Computer viruses are as old as the computers they infect. Already in the middle of the last century it was written about them and, of course, they have not abandoned us. On the contrary, the more we use the more elaborate technology they become, as well as negatives and destroyers.

These are nothing more than harmful softwares that are introduced into computer systems with criminal intentions or, at least, annoying to the user .

From the most basic ones to the floppy disk hit by force to those that only require a mouse click a millimeter higher or lower deliberately done by the user that will be affected, let’s see everything about malware.

What are computer viruses? Definition and examples

Como funciona y actua un virus informatico

Computer viruses are software, programs, with a malicious objective that leads to the alteration in the operation , in one way or another, of a computer device, without its user being aware of much unless you have given your conscious consent for it.

Its operation is quite simple, as is its programming (currently). The basis is the execution of software infected with malicious code programmed for a specific purpose . This execution causes the effects of the code to be triggered, which are very diverse and can be given automatically or programmed.

Among its common features we have:

  • They require a significant consumption of resources, which causes the communication to be cut, data to be damaged or equipment to be slowed down.
  • They are disseminated by copies and replicas. The Internet, of course, makes this characteristic a brutal evil, because, without connection, all the damage remains in our equipment but when it is connected it spreads throughout the world the evil has (if the virus has been programmed for it) .
  • Your goal is always harmful to those who have been infected, either directly or indirectly.

Generally, the first action of these is propagation . This is achieved by sending emails automatically or by joining programs that allow such propagation.

In general, what they do, regardless of whether they have already spread or not, is as follows:

  • Make teams slower (this is a collateral damage to the high resource consumption of many of them).
  • Decrease space from our hard drive.
  • Launch windows in your operating system to leave it disabled by the user .
  • Launch messages that will execute programs automatically .
  • Install softwares that have been previously modified without your consent.
  • Generate and launch more misleading messages to get new clicks and, with it, spreading the computer virus.
  • Corrupting files hosted on our device, from which we are adding at will to those that are vital for its operation.
  • Download junk content .
  • Restart your computer (or turn it off) again and again.
  • Call contacts and other numbers with additional cost.
  • Delete the information stored on the hard disk.
  • Memorize (or, directly, send in real time) information that the user generates or visits.
  • Block networks .

They reach our teams in two ways:

  • Someone (or something) specifically sends it to us as users . They reach us through the mail of infected friends or other people’s profiles on various platforms. These emails or messages we receive are automatic, our acquaintance has not sent anything consciously; We click believing that our acquaintance sends us something in good faith. Another way to send us this malware is through emails, this time from strangers, that encourage us to click on them with different decoys.
  • It is we who “look for it” . There is also the case in which it is we who are looking for something specific on the network and we run into a corrupt file (or even a whole website), so we end up executing it believing it is something else.

His study and knowledge of these already took place before reaching the middle of the century, being John von Neumann a lecturer who spoke of “self-replicating computer software” and who published a work , which was an essay, in which it was stated how a program can be designed so that it reproduces itself. This is how the first virus in history was created.

John von Neumann y los virus en informatica

Interestingly, the next milestone in this topic is with the creation of a game in which one program must compete with another to control it by overwriting it or rendering it useless.

Then we have the creation of a virus by the well-known Siemens , who programmed it in Assembler to achieve a deep analysis of it that would allow a thorough and thorough description to capture it in an article.

Other highlights are the “premonition” of J. Brunner in his novel « The rider of the shock wave «, published in 1975, where he talks about the risk of these evil programs and their possible impact, the comparison of Jügen Kraus makes these, in a university thesis in 1980, regarding biological viruses or the first programming of a malware carried out by a minor, aged 15, whose implementation was run by Apple and that it is considered the first virus of both boot expansion and that it had a real expansion, that is, that it spread outside a theoretical environment or a test.

Characteristics and classification of computer viruses

Depending on the element they infect, we can make a simple classification that includes file-infecting cyber viruses , sector or boot system infecting viruses and Multipartite virus.

File Infectors

Very well defined, they work on the files that we have in our system, both those of origin and those that we are introducing through external devices or downloads.

In turn we can divide them into:

  • Resident viruses: These remain in our latent devices, making use of a small part of our RAM, waiting for the opportune moment to act on the files.
  • Direct action virus: They will infect your files when they are booted.

Boot sector infectors

These remain in the boot sector of the equipment, on the hard disk, this being their switchboard to launch the attacks


These can work indifferently in any of the above ways and are more dangerous due to their nature of being unpredictable.

How do these cyber viruses actually work and what types are there according to their behavior?

Caracteristicas virus ciberneticos de Internet

On the other hand, we can classify them, this time a little more specifically, according to their behavior. Thus, we find those who are uniform, furtive, overwriting, encryption, oligomorphic, polymorphic and metamorphic .


They are self-replicating , playing uncontrollably and affecting the equipment exponentially.


They act so that the user is not aware of their presence because the symptoms remain hidden . This may be temporary and appear when there is already significant damage or that they never show symptoms until they fulfill their mission.


Make use of your code to, once infected a file, overwrite it at will . In this way, not only a harmful element is installed in our equipment but we lose the functionality of the one it occupies, which becomes a kind of zombie.


They work by encrypting your code , either in its entirety or only part of it. In this way, it is more difficult to analyze and discover them. This encryption can be of two types.

  • Fixed encryption: Each new copy of the virus has the same key.
  • Variable encryption: The encryption code is changing to each new copy, so it is more difficult to locate them.


They have a few functions and choose between them, randomly, which one to use to stay and operate by infecting the equipment in question.


For each replica they change their routine, changing sequentially to create harmful copies that, for more inri, are different . This implies that they are really difficult to detect and, therefore, cause great damage until we realize their existence and, even more, until we manage to eliminate them.


They have the ability to rebuild their code as each replica is done.

What types of computer viruses are there and which are the most dangerous?

tipos de virus informáticos

Attending to these as products with their own identity, we have to find several types of computer viruses. The ones we will see next are those considered pure, although, we are currently running into hybrid malicious software , with characteristics of each other.

Boot or boot

Of specific name, is a malware that will infect the partition destined for our operating system to start , activating when we turn on the computer and the OS is loaded.


What it does is link the actions to different files so that, at the moment when a software loads the file in question, executing its instructions , it gives priority to those related to malware ; that is, the virus runs first.

They have similar characteristics to others such as, for example, their code is reproduced when an X situation occurs, is capable of causing physical damage, gives specific messages or emulates any other software; it’s all about the programming that is given to him.

Time bomb

They are the ones that, regardless of their objective, work from an activation that is programmed to be given at a specific time.


What they do is enter your computer without you noticing, disguised as something else which has an extra code , which is this malicious software. Their goal is to collect data and, after obtaining it, they send it, from the device itself, through the network, to a third party.

The Trojan used to be installed from the performance of another malware installer virus . However, this is no longer done that way but it is the user himself who, without knowing it, installs it when executing files that we have downloaded.

A pure Trojan is not replicated, that is, it will not multiply or infect more files; the only way you can have several is to have executed them one by one, either because they are sent to you or because they are posted on the internet and you download them.


Are those whose objective is its propagation, its replica, even without affecting the systems . This also occurs, without it being necessary to affect file by file, the propagation is carried out by execution. There are those that only fill your equipment and other more sophisticated ones that can also be sent by email, making the contagion happen in all directions.

The main intention is simply to publicize this evil and, with it, the ability of cybercriminals, possibly seeking to create panic and to be taken into consideration , preparing the ground for a subsequent attack with another type of malware.

Even so, some, in addition to a very fast propagation, also have a destructive character, being able to damage files or even delete them. In any case, they take their name for the ease of removal and multiplication, the work vision and the coexistence of a good handful of worms being very graphic.


They take control of what happens in your browser , changing the homepage and making it fixed, making it appear in windows or popups in a very invasive way and even making it impossible for us to enter certain sites, being the special place of covering any space with antivirus software , making it difficult for you to get rid of it.


Its essence is Trojan, by the method in which it leads to your system. After running, they remain in your system without making an appearance, so that you don’t know that they are there. What they do is to memorize what you type, with the main intention of obtaining passwords and usernames or accounts to access.

Its transformation is increasing and we already encounter those who record the pages that are visited and the keyboard pointer, knowing, in fact, as screenloggers .


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