What is Virus? Major Types of Viruses



Computer Virus

A computer virus is a piece of code which is capable of copying itself and typically has a detrimental effect, such as corrupting the system or destroying data

Major Types of Viruses

The main types of viruses (Malware) are as follows:

  • Trojan Horse
  • Spyware
  • Adware
  • Worms
  • Bootsector Viruses
  • Time bombs
  • Boot Sector Virus
  • Browser Hijacker
  • File Infector Virus
  • Polymorphic Virus
  • Macro Virus
  • Web Scripting Virus

Trojan Horse

A Trojan horse, or Trojan, in computing is a generally non-self-replicating type of malware program containing malicious code that, when executed, carries out actions determined by the nature of the Trojan, typically causing loss or theft of data, and possible system harm.


Spyware is software that aids in gathering information about a person or organization without their knowledge and that may send such information to another entity without the consumer’s consent, or that asserts control over a computer without the consumer’s knowledge.

“Spyware” is mostly classified into four types: system monitors, trojans, adware, and tracking cookies. Spyware is mostly used for the purposes of tracking and storing Internet users’ movements on the Web and serving up pop-up ads to Internet users.


Adware, or advertising-supported software, is any software package which automatically renders advertisements in order to generate revenue for its author. The advertisements may be in the user interface of the software or on a screen presented to the user during the installation process. The functions may be designed to analyze which Internet sites the user visits and to present advertising pertinent to the types of goods or services featured there.


A computer worm is a standalone malware computer program that replicates itself in order to spread to other computers. Often, it uses a computer network to spread itself, relying on security failures on the target computer to access it. Unlike a computer virus, it does not need to attach itself to an existing program.Worms almost always cause at least some harm to the network, even if only by consuming bandwidth, whereas viruses almost always corrupt or modify files on a targeted computer.

Boot Sector Virus

A boot sector virus is a computer virus that infects a storage device’s master boot record (MBR). It is not mandatory that a boot sector virus successfully boot the victim’s PC to infect it. As a result, even non-bootable media can trigger the spread of boot sector viruses. These viruses copy their infected code either to the floppy disk’s boot sector or to the hard disk’s partition table. During start-up, the virus gets loaded to the computer’s memory. As soon as the virus is saved to the memory, it infects the non-infected disks used by the system.

The propagation of boot sector viruses has become very rare since the decline of floppy disks. Also, present-day operating systems include boot-sector safeguards that make it difficult for boot sector viruses to infect them.


Browser Hijacker

A browser hijacker is spy or malware, commonly available as a Web browser add-on, that changes a Web user’s browser settings in order to change the default home, error or search page. It may redirect the user to unwanted websites while capturing sensitive private data for personal or business gain.

When a browser hijacker is not removed, the infected Web browser may default to the malware browser settings after every reboot, even if the settings are manually readjusted.

File Infecting Virus

A file-infecting virus is a type of malware that infects executable files with the intent to cause permanent damage or make them unusable. A file-infecting virus overwrites code or inserts infected code into a executable file. This type of virus can infect a number of operating systems, including Macintosh, Windows and Unix.

Polymorphic Virus

A polymorphic virus is a complicated computer virus that affects data types and functions. It is a self-encrypted virus designed to avoid detection by a scanner. Upon infection, the polymorphic virus duplicates itself by creating usable, albeit slightly modified, copies of itself.

Polymorphism, in computing terms, means that a single definition can be used with varying amounts of data. In order for scanners to detect this type of virus, brute-force programs must be written to combat and detect the polymorphic virus with novel variant configurations.

Macro Virus

 A macro virus is a computer virus that replaces a macro, which is what enables a program to work and instigates a designated group of actions and commands. When these actions and commands are replaced by a virus, this can cause significant harm to a computer.
Macro viruses can be built into sophisticated applications such as those present in word processors in order to run programs so that they can be launched automatically. Because macro viruses replace prompt commands, word processors are especially vulnerable to these types of viruses. The language is built into the macros in order to hijack the commands, including necessary actions like opening up a document. Thus, through the simple action of opening a document, a macro virus can be launched. Macro viruses may be spread through email attachments, modems and on the Internet, networks, and disks.

Web Scripting Virus

A web scripting virus is a type computer security vulnerability through websites that breaches your web browser security. This allowes the attackers to inject client-side scripting into the web page. It can bypass access controls, steal your information from your web browser. Web scripting viruses are usually used to attack sites with large populations such as social networking, user review, and email. Web scripting viruses are able to propagate a bit faster than other viruses. A common version of web scripting viruses are DDoS. It has to the potential to send spam, damage data and defraud users.


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