Computer virus

Biological Viruses possess both living and non-living characteristics. So, viruses are called connecting link between non-living and living. The unique characteristic that differentiates viruses from other organisms is the fact that they require other organisms to host themselves in order to survive, hence they are deemed obligate parasites. Viruses can be spread in the following exemplar ways:

  • Airborne:  Viruses that infect their hosts from the open air
  • Blood Borne: Transmission of the virus between organisms when infected blood enters an organisms circulatory system
  • Contamination: Caused from the consumption of materials by organisms such as water and food which have viruses within.

Viruses are divided into two categories on the basis of genetic materials: DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid). The bacteriophage is the example of DNA virus. The water of river Gangage can be kept fresh for long time due to bacteriophage viruses present in it. These viruses destroy water stinging bacteria. The TMV (Tobacco Mosaic Virus) is the example of RNA bacteria. It has power of self-replication. Viruses have capacity of replication in living host.

The computer viruses are not biological viruses which cause influenza, aids (Acquired Immune Deficiency Syndrome), mumps, measles, rabies, and other several diseases. It is a pure computer program used to destroy other program. The destructive computer programs are called computer viruses due to its self-replication power like as biological virus.


1. Computer virus



A virus is a program designed to corrupt other programs and alter the way those program works. The impact of a virus can range from making your computer crash when a certain key or series of keys is pushed, to deleting important files, and to the extreme: possibly rendering your computer inoperable. The concept of viruses dates back to 1949, when John Von Newman submitted a paper putting forward the concept of “Self Replicating” program; the idea seemed impossible and was dropped.

The first viruses like program appeared in the form of the recreational game called “CODE-WAR” at the Bell Labs of America Telephone and Telegraph Company”, but first commercial virus was apperead in 1985, when two Pakistani brothers , in order to keep track of software piracy used- Brain Virus on their low cost software sold from their outlet in Lohore. The term computer virus is given by Fred Cohen. Viruses affect some files with following extension:

  • .exe
  • .com
  • .sys
  • .drv
  • .ovr
  • .ovi
  • .ovl
  • .bin and many other files


2. Worm



Computer worms are programs that reproduce and run independently and travel across network connection. It is a sub-class of computer virus. It has ability to travel without any help from person. It has also replication power like as virus. It also infects computer system like as virus. The main difference between viruses and worms is the method in which they reproduce and spared. A virus is dependent upon a host file or boot sector, and the transfer of files between machines to spread. While a worm can run completely independently and spread of its own accord through network connections.

The worm named ‘Homer’ is released in April 1997. It is the first network worm virus using the File Transfer Protocol (FTP) for propagation and infection. In 2003, a worm called Slammer was coded. It has infect hundreds of thousands of computers in less than three hours. The worm ever wreaks havoc on business worldwide, knocking cash machine offline and delaying airline flights. It holds the ranking as the fastest spreading computer worm ever.


3. Spyware



Spyware is an adware (advertisement software) used by programmer or authors to make money, other than by selling it to the users. Spyware has been known to slow down computers with their semi-intensive usage of processing power, bringing up annoying pop-up windows.


4. Logic Bomb



A logic bomb is a program which is activated when certain conditions are met. Some software companies develop logic bombs to prevent piracy of software also. Logic bombs may reside within standalone programs or they may be a part of worms or virus. A variation of the logic bomb is the time-bomb that explodes at a certain time. An example of a time bomb is the infamous Friday the 13th virus.


5. Trojan horse



The term Trojan is derived from the classical myth of the Trojan horse. Towards the end of the siege of Troy, the Greeks left a large wooden horse outside the city. The Trojans, convinced that is was a gift, moved the horse to a place within the city walls. As it turned out the horse was hollow and had Greek solders hiding inside it. These solders then opened the city gates of Troy that night, making it possible for the Greek army to pillage the city. A Trojan is a malicious program that us disguised as legitimate software. It masquerades as a benign application. Unlike viruses, Trojan horse do not replicate themselves, but they can be just as destructive. There are many types of Trojan horse, some are following:

(i) Remote Access Trojan

(ii) Data Sending Trojan

(iii) Destructive Trojan

(iv) Proxy Trojan

(v) FTP Trojan

(vi) Security Software disabler Trojan

(vii) Denial-of-service attack (Dos) Trojan


6. History if Viruses



The concept of computer viruses was started with the mark I computer which electronic circuit was blocked by small moth, and this problem was termed as bugs by Murray Hopper. The term bug is very popular among computer users.






Rear Admiral Grace Murray Hopper discovers a moth trapped between relays in a Navy computer. She calls it a “bug”, a term used since the late 19th century to refer to problems with electrical devices. Murray Hopper also coined the term “debugging” to describe efforts to fix computer problems.



Hungarian scientist John on Neumann (1903-1957) has presented project related with self-replicating programs, providing the theoretical foundation for computers that holds information in their memory.



Engineers at Xerox Palo Alto Research Center discover the computer ‘Worm”, a short program that scours a network for idle processors. Designed to provide more efficient computer use, the worm is the ancestor of modern worms – destructive computer viruses that alter or erase data on computer, often leaving files irretrievably corrupted.



Apple Viruses 1,2 and 3 are some of the first viruses “in world” or public domain. Found on the Apple II operating system, the viruses spread through Texas A&M via pirated computer games.



(a) The FBI busts the “414s”, a group of young hackers who break into several U.S. governments networks, in some cases using only an Apple II+ computer and a modem.

(b) University of Southern California doctoral candidate Fred Cohen has completed his doctoral dissertation on computer virus and coined the term “computer virus” to describe a computer program that can “affect other computer programs by modifying them in such a way as to include a (possibly evolved) copy of itself.” Anti-virus makers later capitalize on Cohen’s research on virus defense techniques.



One of the first PC commercial viruses ever created, “The Brain”, is released by two brothers (Basit and Amjad Alvin) in Pakistan.



Vienna virus was prepared in this year.



One of the most common viruses, “Jerusalem”, is unleashed. Activated every Friday the 13th, the virus affects both .EXE and .COM files and deletes any program run on that day. An Indonesian programmer releases the first anti-virus software for the brain virus. The “Internet Worm” is released and crashed 5000 computers.



The Datacrime and FuManchu are notorious viruses of this year. In this year, IBM released the first commercial anti-virus products. Intensive anti-virus research commences. The “Dark Avenger” virus appears.



Symantec launches Norton Antivirus, one of the first anti-virus programs developed by a large company. Bulletin Boards (BBS) become a common way for virus writers to share code.



(a) A programmer Philip Zimmerman releases “Pretty Good Privacy” (PGP), a free, powerful data-encryption tool. The U.S. government begins a three year criminal investigation on Zinunerman, alleging he broke U.S. encryption laws after his program spread rapidly around the globe. The government later drops the charges.

(b) Symantec releases the Norton Anti-Virus software.



There are 1300 viruses in existence. The Michelangelo scare predicts 5 million computers will crash on March 6. Only 5,000-10,000 actually go down.



Inexperienced e-mail users dutifully forward an e-mail warning people not to open any message with the phrase “Good Times” in the subject line.  The missive, which warns of a virus with the power to erase a recipient’s hard drive, demonstrates the self-replicating power of e-mail virus hoaxes that continue to circulate in different forms today.



Microsoft Corp. releases Windows 95. Anti-virus companies worry that the operating system will be resistant to viruses. Later in the year, however, evolved “Macro” viruses appear that are able to corrupt the new Windows Operating system.



Homer is released in April 1997. It is the first network worm virus using the File Transfer protocol (FTP) for propagation and infection.



Currently harmless and yet to be found in the wild, StrangeBrew is the first virus to infect java files. The virus modifies CLASS files to contain a copy of itself within the middle of the file’s code and to begin execution from the virus section.



The infamous “Melissa” virus infects thousands of computers with alarming speed, causing an estimated $80 millions in damage and prompting record sales of anti-virus products. The virus starts a program that sends copies of itself to the first 50 names listed in the recipient’s Outlook e-mail address book. It also infects Microsoft word documents on the user’s hard drive, and mails them out through Outlook to the same 50 recipients.



The Love Bug, also known as the I Love you, and Love Letter virus has infected a millions of computers virtually overnight, using a method similar to the Melissa virus. The virus also sends password and usernames stored on infected computers back to the virus’s author. Authorities trace the virus to a young Filipino computer student who goes free because the Philippines have no laws against hacking and spreading computer viruses. The spurs the creation of the European Union’s global Cybercrime Treaty.



The Anna Kournikova virus, also known as VBS/SST, which masquerades as a picture of Tennis Star Anna Kournikova, operates in a similar manner to Melissa and The Love Bug. It spreads by sending copies of itself to the entire address book in Microsoft Outlook.



The Klezworm infects executable by creating a hidden copy of the original host file and then overwriting the original file with itself. The hidden copy is encrypted, but contains no viral data. The name of the hidden file is the same as the original file, but with a random extension.



The “Slammer” worm infects hundreds of thousands of computers in less than three hours. The worm ever wreaks havoc on business worldwide, knocking cash machines offline and delaying airline fights. It holds the ranking as the fastest-spreading computer worm ever.



The “MyDoom” worm because the fastest-spreading e-mail worm as it cause headaches – but very little damage – almost a year to the day after Slammer ran rampant in late January 2003. MyDoom uses “social engineering” or low-tech psychological tricks, to persuade people to open the e-mail message sent earlier has failed, and prompts the user to open the attachment to see what the message text originally said. Many people fall for it.

7. Types of Virus



Generally, computer viruses are classified on the basis of files which are corrupted by viral infection.

  • Boot Infectors: The FAT (File Allocation Table) contains list of all the directories-and files present in computer system. It tells the system where the different files are located. The boot infector viruses attack to FAT and change location of files and corrupt files name. Pakistani brain or Basit, Disk Killer, Alameda, Ping pong etc are well known boot infectors. Some boot infectors are Polyboota, antiAEXE etc.
  • System Infectors: System infector viruses affect .exe or .com extension files of computer system. Zerobug, Alabama, Dark Avenger, etc are system infector viruses.
  • Macro viruses: Macro viruses infect files that are created using certain applications or programs that contain macros. These include Microsoft Office documents (MS Word document, MS Excel spreadsheet, PowerPoint presentations, MS Access database) and other similar application files such as CorelDraw, AminoPro etc.
  • General Executive program Infectors: These types of viruses are hidden in all types of application programs, and activated when programs are activated.
  • Network Virus: This kind of virus is proficient in quickly spreading across LAN (Local Area Network) or even over Internet. Usually, it propagates through shared resources, such as shared drives and folders. Once it infects a new system, it searches for potential targets by searching the network for other vulnerable systems. Once a new vulnerable system is found, the network virus infects the other system, and thus spreads over the network. Some of the most notorious network viruses are Nimda and SQLSlammer.
  • E-mail viruses: An e-mail virus could be a form of a macro virus that spreads itself to all the contacts located in the host’s e-mail address book. It any of the e-mail recipients open the attachment of the infected mail, it spreads to the new host’s address book contracts, and then proceeds to send itself to all those contracts as well. The most common and destructive e-mail virus is the ILOVEYOU virus.


8. Some Computer viruses



Computer viruses are self-replicating destructive programs, so these are numerous like biological viruses.

Some important computers viruses are:

Alameda, Alfa, April First, Bosh, Cascade, Charas, Columbus day, Denzuk, Dir-2, Dong-2, ExeBug, Flip, fu-Manchu, Gravity, Green Caterpillar, Gumnam, Hong-Kong, Jerusalem, Joshi, Kanishka,Lehigh-1, long-1, Monkey, Mubarak, Mummy, Ping-Pong, Taiwan, Trikal, etc.


9. Prevention



“Prevention is better than cure”. It is a good practice to follow some simple precautionary measures which can reduce the possibility of a virus attack.

The precautionary measures arc:

  • The CHKDSK command can be incorporated to the AUTOEXEC.BAT to check the disk.
  • The use of pirated software should be stopped.
  • Write protect tags should be used on the original software diskettes.
  • Proper backup of all data and program should be kept.
  • Used floppies should be reformatted before use.
  • Avoid letting the system to be used by unauthorized users.
  • Restrict the use of outside floppies.
  • Copying of files should be done carefully, a better practice is to write the copy command and in a batch file with CHKDSK command.


10. The Cure



The viruses are not omnipotent. Viruses can be cured with anti-viral program. John McAfee founded ”CVIA(Computer Virus Industry Association)” to produce anti-virus software.

The anti-virus software performs one or more of the following functions:

  • Prevention: ”Prevention is better than cure”. The prevention is the best way to protect computer programs from viral attack. It is a concept of security gate and it protects computer system from entry of viruses. There are many preventive measures for security purposes.
  • Detection: The detector is loaded into computer system, it warns about computer viruses. It checks executable and other files and display messages.
  • Vaccination: The term vaccine is very common, and it is used in medical science and used as preventive technique from several communicable dieses. The vaccine is the particle of dead or weakened virus, injected into body to produce antibodies against specified dieses. This term is borrowed in computer science also. The vaccinators insert some codes into executable files. If any changes take place in files, it displays warning message.
  • Inoculation: Inoculators inject the virus signature into infected files or area at appropriate location. When viruses get these injected signature at the time of replication believe that the files are already infected and so do not infect files. In this way, virus cheating technique is known as inoculation.
  • Identification: Identification is also warning message displaying technique when any virus is detected in memory or files.
  • Damage Control: The better equipped anti-viral programs controls damages. They may be preventive or restorative.

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