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Computer viruses are simply the programs which infect our computer hardware and software. They are not biological viruses. They are developed by using programming language. Computer viruses are the man-made small malicious programs that disturbs the normal functioning of the computer in many ways. Viruses are capable of reproducing themselves and capable of causing great harm to data or other programs on the computer system. They may damage data and software in the computer. Viruses also produce several unusual symptoms in our computer and gives trouble to the user while working with computer. They irritate the user by showing unexpected behavior in the computer screen. At the first time, computer viruses was created by the computer programmers to give entertainment for computer users by displaying different funny messages on the screen.

We can define computer viruses in the following ways:
Computer virus is a small malicious program capable of reproducing itself and causes great harm to data or other programs on the computer system.
A computer virus is an illegal, self-replicating destructive program that disturbs the normal functioning of the computer in many ways.
A computer virus is a  program. a block of executable code, which attaches itself to, overwrite or otherwise replaces another program in order to reproduce itself without a knowledge of a computer user.

Evolution of Computer Viruses and Anti-virus

The roots of the modern computer viruses go back to 1949 when Hungarian mathematician, JOHN VON NEUMANN introduced the concept of replicating computer program. He presented a paper on the "Theory and Organization of Complicated Automata," in which he postulated that a computer program could reproduce. This theory was tested in the 1950's at Bell Laboratories when a game called "Core Wars" was developed, in which players created tiny computer programs that attacked, erased and tried to propagate on an opponent's system. In 1983, American electronic engineer FRED RICK COHEN first introduced the term "COMPUTER VIRUS" to describe a self-replicating computer program. In 1987 two Pakistani brothers AMJAD and ALVI created the world's first PC virus named "C-Brain". The brothers created the virus to stop pirated copies of software software developed from Alvi's Brain Computer Shop. This virus spread worldwide by 1987.

In 1988 two new viruses appeared: Stone, the first bootstrap-sector virus and the Internet worm, which crossed the United States overnight via computer network. Computer viruses grew more sophisticated in the 1990's. In 1995 the first macro language virus, WinWord Concept, was created. In 1999 the Melissa macro virus, spread by e-mail, disabled e-mail servers around the world for several hours and in some cases several days. The "I LOVE YOU" virus introduced in 2000. It is the world's most prevalent and costly viruses. By the time the outbreak was finally brought under control, losses were estimated at US$10 billion and is said to have infected 1 in every 5 PCs worldwide.

Now-a-days the number of computer viruses are increasing day by day. Today there are thousands of viruses. Different viruses show different symptoms on the computer. As virus creators become more sophisticated, they learned new tricks: One important trick was the ability to load viruses into memory so they could keep running in the background as long as the computer remained on. This gave viruses a much more effective way to replicate themselves. Another trick was the ability to infect the boot sector on hard disks.

Programmers develop antivirus software to protect computer from viruses. Antivirus software is a kind of software that detects and removes viruses from the computer. In computer history, there is not reliable data about who developed first antivirus software and when. The first publicly-known antivirus was produced by Bernt Fix in early 1987. In 1988 AIDSTEST and AntiVir were released. Peter Norton made a number of contributions to the growing field of virus detection. He developed Norton Anti-virus in 1992. It is one of the most popular antivirus software till date. Some most advanced anti-virus software being used nowadays are: Kaspersky, Avast, Norton, etc.

Cause of Creating Computer Viruses

Number of computer viruses are increasing day by day with the increase in the usage of the Internet. There are thousands of types of computer viruses with their unique cause of creation showing different symptoms on the computer respectively.

People create computer viruses for many purposes. The main cause of making computer viruses are as follows:

  • To stop the software piracy, the software developers themselves create computer viruses to stop illegal reproduction of software.
  • To steal sensitive information such as personal details, credit card numbers, bank account numbers, passwords, data, etc. 
  • To earn money by selling anti virus.
  • To take control of a computer and use it for specific tasks.
  • To show programming skill and talent. To give entertainment to the computer users by displaying funny messages or pictures on the screen.

Symptoms of Computer Virus

Today, there are thousands of computer viruses and the numbers of computer viruses increasing daily. These viruses show different symptoms in the computer. Some viruses create problems in application files, some change the location of file, some hide files, some reduce memory size and some produce unnecessary messages on the screen and so on. Some of the common symptoms of computer viruses are as follows:

  1. Viruses reduce the memory space of computer.
  2. Viruses change the size of computer files.
  3. Viruses change the location and extension of files.
  4. Viruses may slow down computer systems and reduce computer's ability to work.
  5. Viruses change the sequence of program instructions so that computer cannot perform task according to user's instructions.
  6. Viruses delete the some portion of data from the database.
  7. Viruses show unusual error messages frequently on the computer screen.
  8. Viruses open programs automatically without giving instruction.

Types of Computer Viruses

On the basis of their ways of infecting, viruses can be categorized into various types. Among them some common types of viruses are described below.
  • Boot Sector or Start up Infector Virus: It is also called Boot record infectors virus. Start up infector virus infects the boot record or Master Boot Record (MBR) of the disk and replace the boot record program, copy elsewhere or overwrite it. This type of virus is loaded during the booting time and create the bad sectors on the disk and affect the entire computer system. This virus generally hides in the boot sector, in either the bootable disk or the hard drive.

  • Boot Infector or Operating System Infector Virus: This is a common type of computer virus which infects the various parts of the Operating System or Master Control Program (MCP) and deletes and corrupts the system files necessary for booting. Thus, when these files are corrupted the Operating System cannot be loaded.

  • Application Program Infector or File Infector Virus: These viruses infect the executable files or programs. An executable file can be a program file, like Word or Excel, Access, etc. They attach themselves to executable programs, such as word processors, spreadsheet applications and computer games which has usually .EXE or .COM extensions. These viruses directly attack and modify application program files. When an infected executable file is run, the viruses executes and does whatever it wants to do.

  • Message Carrying Virus: This type of virus does not do any harm to the computer but it frequently displays the unwanted, vulgar message on the screen to irritate the user. It may be used to provide entertainment to the user in some extence.

  • Polymorphic Virus: This type of virus encrypts its code in various ways and appears differently in each infection. Polymorphic viruses are harder to identify since each copy of the virus is different. Phoenix, Stimulate, Evil, Virus 101, proud and Cascade, etc are some examples of polymorphic viruses. They are also difficult to identify and remove by anti virus.

  • Macros Virus: This type of virus infects the user related macros in application software with in a document or template. it is activated when we open the Word or Excel program and it affects the normal program and attaches itself.

  • Multipartite Virus: These are the hybrid of Boot and program viruses. They infect the program files at the time of execution. Similarly, it is loaded at the booting time and starts infect the computer program.

  • Worm: Worm is a self replicating or propagating virus that mainly damages the computer system. It is activated itself and makes multiple copies and fills the entire disk with copies of itself. It is basically spread through the network and Internet via email message attachments. Unlike a virus, it does not need to attach itself to an existing program.

  • Stealth Virus: A stealth virus is a file virus, that uses special techniques to hide its presence from users and virus scanners.

Sources of Computer Virus

Computer viruses are those programs which are capable of reproducing themselves and capable of spreading from one computer to other through different media. Viruses hide themselves in other files and folders and they easily transfer along with the infected files or folders without the knowledge of a user. For example, an e-mail virus travels as an attachment to e-mail messages and usually replicates itself by automatically mailing itself to dozens of people in the victim's e-mail address book. Nowadays, Internet is being the main means of spreading computer viruses all over the world. The most common ways of spreading computer viruses are as follows:
  1. E-mail
  2. Internet 
  3. Intranet
  4. Virus Infected Portable Disks (such as external hard-disk, pen-drive, etc.)
  5. Pirated Software and Games CD's

Methods to Protect Computer from Virus

Viruses main mission is to spread out and then get active. Some viruses just spread out and never activate. Viruses when spread out, they make copies of self. Computer viruses spread from one computer to other through E-mail, Internet, USB drive (pen drive),floppy disks, CD/DVD and other storage devices. Computer viruses cause a great harm in our computer system. Viruses irritate us while using computer by showing unexpected behavior in the computer, Annually, millions of dollars are lost throughout the world due to the viruses. So, it is necessary to protect our computers from the viruses. As there is saying "prevention is better than cure" so we should follow the safety measures in order to protect our computer from viruses.

The following are the common preventive measures from computer viruses.
  1. Keep your software(Operating System such as Mac, Windows and Linux)up to date to fix bugs that could potentially be exploited by hackers.
  2. Not to open any E-mail(G-mail) attachment files before scanning it and don't click on links within emails if you don't recognize the sender of that email.
  3. Install free(No need to pay for an annual subscription) Anti-virus software from a well-known reputable company (such as Kaspersky Lab and Avast or  built-in Windows Defender will do the job perfectly for Windows) and scan computers regularly for viruses.
  4. Update antivirus software regularly through the Internet in order to get the latest virus definition because new viruses are developing day by day.
  5. Keep backup of data and programs on a regular basis to prevent data loss.
  6. Always lock the computer using strong password and avoid using same password for everything instead,use a free service like lastPass to create and manage your passwords.
  7. Make sure if you have enabled built-in firewall to maximize your online protection.
  8. Make sure your Web browser’s(Google Chrome) security settings are high enough to detect unauthorized downloads and have the ability to stop pop-up windows which allow you to set the security for accepting pop-ups.
  9. Not to download any programs from the unknown website of the Internet unless you are confirmed that they are virus free.
  10. Not to use any pirated software because there is most probability of viruses with pirated software CD's
  11. Scan the portable disks (such as pen drive, external hard disk) to remove viruses before using it.

Anti-Virus Software

Antivirus is a utility software designed to detect and remove viruses from computer system.
It is a program that prevents computer from viruses. It identifies and removes the viruses, as well as many other types of harmful software, collectively referred to as malware from the computer. It mainly identifies or detects the malicious virus from the disk, kills or heals the virus and quarantines it if necessary. Modern antivirus software can protect computer systems against a wide range of malware, including worms and Trojans. It is compulsory to have an antivirus software in your computer. An anti-virus software should be installed from a well-known reputable company and should scan computers regularly. The antivirus software perform the following key tasks.
  • Scans the files and folders for viruses.
  • Alerts the user when viruses are found and provides the information about the viruses.
  • Automatically cleans the virus-infected files.
  • Monitors the resources of the computer from viruses.
Some of the most popular anti-virus software are as follows:
  • Kaspersky Lab
  • Avast!
  • AVG (Anti-Virus Guard)
  • Bitdefender
  • Avira
  • Norton Anti-Virus (NAV)
  • (Windows Defender)-(Windows 10)
*FREE Version of all the above mentioned antivirus software are available.


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