Schoolans.com

Computer Viruses

Concept: Biggest Threat

           Computer virus is a program or piece of code that is loaded onto your computer without knowledge and runs against your wishes. Viruses can also replicate themselves. Some computer viruses may cause messages to appear on the screen but others are destructive and can wipe out the computer’s memory or even cause more severe damage. It is the intellectual creation of a computer programmer. It can affect a computer without the user knowing it. Viruses can easily hide within a system by attaching themselves to other files or programs because they are small in size. The ability of a virus to replicate enables it to infect files and programs.

       Computer viruses are designed to infect and potentially damage files on a computer that receives it. They are usually activated when the program or file to which it is attached or executed is executed or accessed. Once activated, viruses look for certain programs to infect, depending what they’ve been programmed to do. Viruses can spread through emails, attachments, application programs on your computer, or application programs installed from disk drives. The way in which a virus replicates and spreads from one computer to another depends upon the way it is programmed to behave. Different viruses behave in different ways. Some stay active in memory until the computer is shut down. Other viruses stay active only as long as the infected application is running.

Types of Computer Virus

Computer viruses come in a wide variety. The level of destructiveness of viruses varies widely. Virus behavior can range from annoying to destructive. Computer viruses are categorized by their infection targets. They are of following types: Boot sector viruses and File infecting viruses.

Boot Sector Virus

Boot sector virus is a type of virus that infect computer system by copping code either to the  boot sector on a floppy disk or the partition table on a hard disk. During startup, the virus is loaded into the memory. Once in memory, the virus will infect any non-infected disks accessed by the system. Examples of the boot sector viruses are Michelangelo and Stoned.

        Boot sector viruses are spread to computer system by booting, or attempting to boot, from an infected floppy disk. Even if the disk does not contain MS-DOS system files needed to successfully boot, an attempt to boot from an infected disk will load the virus into memory. The virus hooks itself into memory as if it were a device driver. The virus moves the interrupt 12 return, allowing itself to remain in memory even after a warm boot. The virus will then infect the first hard disk in the system.

Expanding your horizons

Brain is the industry standard name for a computer virus that was released in its first form in January 1986, and is considered to be the first computer virus for MS-DOS. It infects the boot sector of storage media formatted with the DOS File Allocation Table (FAT) file system. Brain was written by two brothers, Basit Farooq Alvi and Amjad Faroow Alvi, from Lahore, Punjab, Pakistan.

File Infecting Viruses

File infecting viruses infect executable program files having an extension .exe, .com, or .dll. These viruses either overwrite or modify the contents of executable files. When these infected files are executed, the virus gets activated and remains present in the main memory even after the execution of the file is over. When another file is executed, this virus attaches itself to the new file and thus another file gets infected. File infecting viruses can spread by using floppy disk, CDs, over the network, or through remote access. The examples of file infecting viruses are Friday 13th, Enigma, Nemesis and Cascade.

Ill-Effects of Virus Infection

       Different viruses can affect a computer system in different ways. The impact of a virus infection can range from disruption in work by flashing messages on a computer screen to causing serious damages worth millions of dollars to an organization. In order to detect a virus attack on your computer, you must observe the computer for signs of changes or strange behavior that may be the symptoms of a virus attack.

Some symptoms of virus infection are listed below:

  • Unwanted message appears on the screen.
  • It takes long time to load the program.
  • It slows down the performance of the computer.
  • The computer runs very slowly.
  • The computer displays pop up messages.
  • The computer system hangs or freezes frequently.

Tips for Safe Computing

     Today, we are more dependent on computers and the information that they store than ever before. From spyware, viruses, and Trojans to identify theft and computer hardware malfunctions-any disruption can have a huge impact on our lives. The spread of computer virus infections can be stopped through the practice of safe computing. The followings are the list of some recommendations for safe computing:

  • Always check a removable disk for viruses before using it.
  • Ensure that your system boots through hard disk first. Remove all removable disks from the drive during boot up.
  • Don’t use illegal software. Illegal software contains virus.
  • Install software from the original optical disk. If the originals are not available, scan the secondary media for viruses before installation.
  • Ensure that the antivirus package scans all the system and boots files at start-up.
  • The automatic virus monitors should be running constantly on your system to ensure that no infected files are transferred to your hard disk over the network.
  • Always scan files downloaded from internet or transferred overthe network before executing them on your machine.
  • Never load an unknown disk into your system unless you make sure it is virus free.
  • Finally, enable the personal firewall on your computer. This will help to keep unauthorized people from the snooping around your computer when it is connected to the internet.

Anti-virus Software

         Anti-virus software is a program or set of programs that are designed to prevent, search for, detect, and remove software viruses, and other malicious software like worms, Trojans, adware, and more. It must be updated frequently for protection against new viruses. It resides in the memory so that it detects the virus at the time of entry and prevents them from doing any damage to the system. Some popular anti-virus softwares being available are: Norton Antivirus, McAfee Virus scan, Microsoft Security Essentials.

Antivirus software typically performs following tasks:

  • Scan files and folders for viruses.
  • Provides information when a virus is detected.
  • Cleans virus-infected files.
  • Continuously monitors memory to protect the computer from memory-resident viruses

Facts Corner =   Antivirus software is important because it specializes in the quarantining and removal of viruses.

McAfee VirusScan

      Kaspersky Anti-virus is an antivirus program developed by Kaspersky lab. It is designed to protect users from malware and is primarily designed for computers running Microsoft windows and Mac OS X. The features of Kaspersky antivirus include real-time protection, detection and removal of viruses, Trojans, worms, spyware, adware, key loggers malicious tools and auto-dialers, as well as detection and removal of rootkits.It also includes instantaneous automatic updates via the “Kaspersky Security Network” service.

Brain Storming Task

  1. Computer virus is a computer program or piece of code that is loaded onto your computer without your and runs against your wishes.
  2. Boot sector virus is a type of virus that infects the computer systems by coping code either to the boot sector on the floppy disk or the participation table on a hard disk.
  3. Antivirus is a program or set of programs that are designed to prevent, search for, detect, and remove software viruses, and other malicious software like worms, Trojans, adware, and more.

Tricky terms

  • Antivirus software: A program designed to detect and remove viruses from the infected programs or files in the computer system.
  • Boot sector: The portion of a disk reserved for the self-starting portion of an operating system.
  • Boot sector virus: A computer virus designed to infect the boot sector of the disk.
  • File infecting virus: A computer virus designed to infect executable program files having extensions .exe, .com, and .dll.
  • Virus: A software program with the ability to reproduce itself.

Let us revise

  • Computer virus is a program or piece of code that is loaded onto your computer without your knowledge and runs against your wishes.
  • Computer viruses are designed to infect and potentially damage files on a computer that receives it.
  • Boot-sector virus is a type of virus that infect computer systems by copying code either to the boot sector on a floppy disk or the partition table on a hard disk.
  • Boot-sector viruses spread to the computer systems by booting, or attempting to boot, from an infected floppy disk.
  • File infecting viruses infect executable program files having an extension .exe, .com, or .dll.
  • The examples of file infecting viruses are Friday the 13th, Enigma, Nemesis and Cascade.
  • Antivirus software is a program or set of programs that are designed to prevent, search for, detect, and remove software viruses, and other malicious softwares like worms, Trojans, adware, and more.
  • Kaspersky anti-virus is designed to protect users from malware and is primarily designed for computer running Microsoft Windows and Mac OS X.
  • Norton antivirus is developed and distributed by Symantec Corporation, provides malware prevention and removal during a subscription period.

Solved Exercise

  1. What is a computer virus? What are the different types of computer viruses?

Ans. Computer virus is a program or piece of code that is loaded onto your computer without your knowledge and runs against your wishes.Computer viruses are categorized by their infection targets. They are of the following types: boot sector viruses and file infecting viruses.

2.What is a file infecting virus? Give any two examples of it?

Ans. File infecting virus is a computer virus that infects executable program files having extensions .exe, .com, or .dll.It can spread by using floppy disks, pen drives, and CDs. Friday the 13th, Enigma and Nemesis are examples of file infecting virus.

3. What are the ill-effects of a computer virus?

The ill-effects of a computer virus are listed below:

Ans. The ill-effects of a computer are listed below:

  • Unwanted message appears on the screen.
  • It takes long time to load the program.
  • It slows down the performance of the computer.
  • The computer runs very slowly.
  • The computer displays pop up messages.
  • The computer system hangs or freezes frequently.

4. List some of the precautions that must be observed to avoid virus infection.

Ans. Some of the precautions that must be observed to avoid virus infection are:

  • Always check a removable disk for viruses before using it.
  • Ensure that your system boots through hard disk first. Remove all removable disks from the drive during boot up.
  • Install software from original optical disk.  If the originals are not available, scan the secondary media for viruses before installation.
  • Don’t use illegal software. Illegal software contains virus.
  • Ensure that the antivirus package scans all the system and boots files at start-up.
  • The automatic virus monitors should be running constantly on your system to ensure that no infected files are transferred to your hard disk over the network.
  • Always scan files downloaded from internet or transferred over the network before executing them on your machine.
  • Scan all e-mail attachments before executing them on your machine.
  • Never load an unknown disk into your system unless you make sure it is virus free.
  • Finally, enable the personal firewall on your computer. This will help to keep unauthorized people from the snooping around your computer when it is connected to the internet.

5. What is an anti-virus program? List some of the popular anti-virus programs.

Ans. . Antivirus software is a program designed to detect and remove viruses from the infected programs or files in the computer system. Some of the popular anti-virus software are: Norton Antivirus, McAfee Virus scan and Smart dog.

Chapter review

  1.  State whether the following statements are true or false.

a. Computer virus is a program or piece of code that is loaded onto your computer without your knowledge and runs against your wishes.{True}

b. File infecting virus is a type of virus that infects computer systems by copying code either to boot sector on a floppy disk or the partition table on a hard disk.{False}

c. The examples of file infecting viruses are Friday the 13th, Enigma, Nemesis and cascade.{True}

d. The pirated software contains viruses.{True}

e. Antivirus software is a program or set of programs designed to prevent, search for, detect, and remove software viruses, and other malicious software like worms, Trojans, adware and many more.{True}

2.  Match the following.

Group A

Boot sector virus

File infecting virus

Antivirus software

Virus

Boot sector

Group B

The computer virus designed to infect the boot sector of hard disk.

A computer virus designed to infect executable program files having extensions .exe, .com, or .dll.

A program designed to detect and remove viruses from infected programs or files in the computer system.

A computer program with the ability to reproduce itself.

The portion of the disk reserved for the self-starting portion of an operating system.

3. Select the best answer from the list of choices.( Answer in bold and italic style)

a) Disk killer, stoned and Michelangelo are the examples of …………….

i) Boot sector virus ii) File infecting virus iii) Email virus

b) The type of virus that is designed to infect executable program files having extensions .exe, .com or .dll is ……..

i) Boot sector virus ii) File infecting virus iii) Script virus

c) The first PC boot sector virus created in 1986 by two brothers, Basit and Amjad Farooq Alvi is ………

i) Brain ii) Disk killer iii) Stoned

d) A program designed to detect and remove virus from the computer system is ……….

i) Malware ii) Freeware iii) Antivirus

e) …………………….. is the popular antivirus software.

i) Microsoft security essential ii) Web browser iii) Microsoft Excel

4. Give the appropriate technical term for the following.

a. A software program with the ability to reproduce itself. (virus)

b. A program designed to detect and remove virus from the infected program or files in the computer system. (Antivirus)

c. The portion of the disk reserved for the self-starting portion of an operating system. (Boot sector)

d. A computer virus designed to infect the boot sector of the disk. (Boot sector virus)

e. A computer virus designed to infect executable program files having extensions .exe, .com, or .dll. (File infecting virus)

5. Answer the following questions.

a. What is computer virus?

Ans. Computer virus is a program or piece of code that is loaded onto your computer without your knowledge and runs against your wishes.

b. How does a computer virus spread from one computer to another?

Ans. Computer virus spread from one computer to another through secondary media, virus infected files, illegal software, e-mail attachment e.t.c.

c. What is boot sector virus? Give any 2 examples of boot sector virus.

Ans. The computer virus designed to infect the boot sector of hard disk is called boot sector virus. Any 2 examples of boot sector viruses are Michelangelo and Stoned.

d. What is boot sector?

Ans. The portion of the disk reserved for the self-starting portion of an operating system is called boot sector.

e. List any 3 ill effects of computer virus.

Ans. Any 3 ill effects of computer virus are:

  • Unwanted message appears on the screen.
  • It takes long time to load the program.
  • It slows down the performance of the computer.

f. List any 3 precautions that must be observed to avoid computer virus infection.

Ans. Any 3 precautions that must be observed to avoid computer virus infection are:

  • Always check a removable disk for viruses before using it.
  • Ensure that your system boots through hard disk first. Remove all removable disks from the drive during boot up.
  • Install software from original optical disk.  If the originals are not available, scan the secondary media for viruses before installation.

By: Prashanna Bhandari and Sudarshan Sigdel

Leave a Comment

Your email address will not be published. Required fields are marked *