What is a Computer Virus? - Definition, Types & Protection

Computer Virus Definition

A computer virus we can say is a small software program or a piece of code that is loaded on your computer system while using internet can spread from one computer to another and running without your knowledge. Computer viruses can also replicate and they are man-made. How the replication done in the computer virus? A simple virus that can make copy of itself over and over again and that would be easy to produce. Sometimes a simple virus is very dangerous because it stored in your system available memory and when after some time all the small virus collected it may halt you system. A virus has a capacity to corrupt the files located in you system and it also has a capability to spread the virus via e-mail program and effect the system other email addresses in your online address book. It can also delete everything on your hard disk that would be the worst case scenario. A virus can also affect your system security. In 1987, A virus infect ARPANET, then the Defense department and other universities using large network, many antivirus programs become available. Such programs are invent because they check periodically you system and prevent it from known viruses.

Types of Computer Virus

Types Of Computer Virus

Macro virus

Macro virus infect the file hat are created from some application or programs which are mainly contain macro files like doc, pps, xls, mdb. So basically such virus infect the files with the macros and also templates and document that are contained in the file. These virus hide in documents that are shared through network and e-mail. Macro virus are Relax, bablas, Melissa.A, 097M/Y2K.

Memory Resident Viruses

Resident viruses activated every time the OS runs and end up infecting other opened files. Such virus usually fix themselves inside the computer memory, hide in RAM. Resident viruses are CMJ, meve, randex, mrklunky.

Overwrite Viruses

Overwrite viruses delete the information from the file partially or completely once it infect a file. It infect only the file content may be change all the content but the file location and name remains the same, means doesn’t infect the file name and the location. Overwrite viruses are Trj.Reboot, way, trivial.88.D.

Direct Action Viruses

Direct Action Virus activate when the file containing virus is executed. The virus take no other action unless an infected file is executed again. Most viruses avoid this because this is not so productive, but such virus damage in the past. Direct Action viruses are Vienna Virus.

Directory Virus

Directory virus is also known by cluster virus and file system virus. This can infect the computer’s directory by changing the path by indication the location. Such virus located into the hard disk but affect the entire directory. Directory viruses are die-2 virus.

Web Scripting Virus

Mostly web pages contain complex code to make their web page content interactive so that such code exploit that cause undesirable actions. Such virus originate from browser and web pages. Web Scripting viruses include JS.Fortnight that spread via malicious emails.

Multipartite Virus

This type of virus spread in multiple ways and the taken action depending upon the type of OS installed and presence of certain files. Most of the time this virus try to hide in computer’s memory not to infect the hard disk. Multipartite Viruses are flip, invader and tequila.

Polymorphic Virus

Polymorphic virus encode and encrypt themselves every time they are going to infect the computer system. For that they use different encryption methods and algorithms. Since they use different encryption method each time which is difficult for antivirus to locate and resolve them. Polymorphism viruses are Marburg, tuareg, Satan bug, elkern.


Worm is very similar to a virus having a capability to self-replicate which is leading to negative effect on your system. This consume too much system memory and also affect web servers and network servers. Worm viruses are lovgate.F, sobig.D, trile.C, PSWBugbear.B, Mapson.

Trojans horses

This name comes from a software which is very useful software but later do damage you system after run once. This virus can track the login details of the users who is online. Example as we all know E-banking is very common, so its vulnerability of tracing your login details whenever your PC is working without the support of strong antivirus.

Email Virus

This virus is spread via email, this will hide an email when recipient opens the mail.

Boot Infectors

This virus type will include boot sector and master boot record types. While all the viral codes are separated because they infect the hard disks or the floppy. It include the viruses like the brain virus which is very first wild virus is to be created.

Virus Protection Methods

Protection of virus is well designed software program which is used in infected computer systems to prevent from viruses, worms and Trojan horses. The main purpose of using Virus protection is to remove any malicious software code which is already infect a computer. Most of the virus protection utilities now bundle anti-spyware and anti-malware ability that belong to anti-virus protection. To secure internet that include some additional capabilities like anti-spam, anti-phishing, firewall, optimization of files and file protection.