Common Types and Symptoms of a Computer Virus

In this article we will go through the different types of common computer infections and the most common signs that your computer is infected

What is a virus?

A computer virus is a program or piece of code that is loaded onto your computer without your knowledge and runs against your wishes. Viruses can also replicate themselves. All computer viruses are man-made. A simple virus that can make a copy of itself over and over again is relatively easy to produce. Even such a simple virus is dangerous because it will quickly use all available memory and bring the system to a halt. An even more dangerous type of virus is one capable of transmitting itself across networks and bypassing security systems.


What is the virus’s goal?

The goal of a virus depends entirely on the person that made it and their intentions at the time. For example, A virus might be made to take advantage of a very specific exploit that is only available on very few computers after certain conditions have been meet, but the systems that have this exploit/hole might be systems that keep very valuable and sensitive information or run a widely used service for lots of other people. In this case the person making the virus would design to take advantage of the exploit to gain access to the data or to control the service that is being provided. This virus would be useless on another computer that is used for a different reason.

These days for people making the virus, they usually want it to be as widespread as possible. To do that they first target the Operating System that is the most used in the world which is Microsoft Windows. This is why there are so many virus’s for Windows Based computers and why it’s so important to take precautions to protect your computer from these viruses.


The most common goals that common viruses have today are…

• Collect data about your computer and the user’s habits and sell that data.

• Hijack your computer to push more Ads to your screen and gain money from advertising

• Hijack your computer and holds your computer for ransom until you pay it or tricks the user into buying fake software.

• To mess up your computer as much as they can, because they can.


While each virus is unique in its own way they can be generalised and put into a category based on how it infects your computer and what the goal of the virus is. Below is a list of different common symptoms your computer may experience and also a list of common types of infections.


The most common symptoms of a computer virus infection are…

• Your computer slows down without any reason.

• Your computer system has less available memory than it should.

• Unknown programs or files are being created.

• Programs or files become missing.

• Corrupted files.

• Your computer restarts in unusual ways.

• Some files or programs suddenly don't work properly.

• Strange messages, displays, music or sounds.

• Changed Hard Drive name or Volume name.

• Hard Drives or Disk Drives are inaccessible.


List of Common types of infections

Boot Sector Virus

The term “boot sector” is a generic name that applied generally to the boot information used by any operating system that is on your Hard Drive. In modern computers this is usually called the “master boot record,” and it is the first sector on a partitioned storage device. Boot sector viruses became popular because of the use of floppy disks to boot a computer. The widespread usage of the Internet and the death of the floppy has made other means of virus transmission more effective. While not as popular as it once was it is still used.


Browser Hijacker

This type of virus, which can spread itself in numerous ways including voluntary download, effectively hijacks certain browser functions, usually in the form of re-directing the user automatically to particular sites. It’s usually assumed that this tactic is designed to increase revenue from web advertisements. There are a lot of such viruses, and they usually have “search” included somewhere in their description. A program called “CoolWebSearch” may be the most well known example, but others are nearly as common.


Direct Action Virus

This type of virus, unlike most, only comes into action when the file containing the virus is executed. The payload is delivered and then the virus essentially becomes dormant – it takes no other action unless an infected file is executed again. Most viruses do not use the direct action method of reproduction simply because it is not prolific, but viruses of this type have done damage in the past. The Vienna virus, which briefly threatened computers in 1988, is one such example of a direct action virus.


File Infector Virus

Perhaps the most common type of virus, the file infector takes root in a host file and then begins its operation when the file is executed. The virus may completely overwrite the file that it infects, or may only replace parts of the file, or may not replace anything but instead re-write the file so that the virus is executed rather than the program the user intended. Although called a “file virus” the definition doesn’t apply to all viruses in all files generally – for example, the macro virus below is not referred to by the file virus. Instead, the definition is usually meant to refer only to viruses which use an executable file format, such as .exe, as their host.


Macro Virus

A wide variety of programs, including productivity applications like Microsoft Excel, provide support for Macros – special actions programmed into the document using a specific macro programming language. Unfortunately, this makes it possible for a virus to be hidden inside a seemingly harmless document. Macro viruses very widely in terms of payload. The most well known macro virus is probably a Word document supposedly containing the passwords to various websites. The virus also exploited Word’s link to Microsoft Outlook feature in order to automatically email copies of itself to others on your contact list.


Multipartite Virus

While some viruses are happy to spread via one method or deliver a single payload, Multipartite viruses want it all. A virus of this type may spread in multiple ways, and it may take different actions on an infected computer depending on variables, such as the operating system installed or the existence of certain files.


Polymorphic Virus

Another jack-of-all-trades, the Polymorphic virus actually mutates over time or after every execution, changing the code used to deliver its payload. Alternatively, or in addition, a Polymorphic virus may guard itself with an encryption algorithm that automatically alters itself when certain conditions are met.The goal of this trickery is evasion. Antivirus programs often find viruses by the specific code used. Obscuring or changing the code of a virus can help it avoid detection.


Resident Virus

This broad virus definition applies to any virus that inserts itself into a system’s memory. It then may take any number of actions and run independently of the file that was originally infected. A resident virus can be compared to a direct payload virus, which does not insert itself into the system’s memory and therefore only takes action when an infected file is executed.


Web Scripting Virus

Many websites execute complex code in order to provide interesting content. Displaying online video in your browser, for example, requires the execution of a specific code language that provides both the video itself and the player interface. Of course, this code can sometimes be exploited, making it possible for a virus to infect a computer or take actions on a computer through a website. Although malicious sites are sometimes created with purposely infected code, many such cases of virus exist because of code inserted into a site without the webmaster’s knowledge.