Page 67 - IT 402 v2.0 class 10
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In a computer system  virus does not evolve by itself  it is uploaded or in ected in a network or into a storage
            media. It is communicable  i.e.  it is transmitted from one computer to another computer or to a network by
            some medium of transmission like     pen drive  external hard disk  software  internet connection  bluetooth
            etc.  hen infected  viruses replicate by themselves.

             here are different types of viruses that infect specific components or specific functioning of a computer
            system.  hey can range in severity. Some may cause mild damages while others can cause severe damages
            to hardware  software or files.  xamples of some common viruses are i ryte  OneInstaller   oobface   ia oor
             rO  c    yte  andit   rain  Small.    Stealth    etc.

            Boot Sector Virus
             ooting is the process of loading operating system in the primary memory from the boot sector.  oot sector is the
            core area of hard disk storage where the most important programs like OS are stored.

              boot sector virus gains complete control over the Master  oot  ecord  M   .  M   is the first sector of the
            computer hard drive that stores the information about loading the operating system into the main memory.
             oot sector virus replaces the location and information of the operating system in order to stop it from
            getting loaded into the main memory  resulting into errors during booting. Michelangelo   olyboot.   Stones
            and  nti    are some common examples of boot sector virus.
            Program File Virus

              program file infecting virus is a type of malware that infects the executable files of a program with the
            intention of causing permanent damage or making the program useless.   file infecting virus overwrites
            the code or inserts infected code into the source of an executable or program file.  hen such programs are
            executed  such virus activates and damages the files.  hen a program runs many times  program viruses
            are deliberately loaded in a program by the developer.   program file infecting virus is also known as a  File
            In ector . Sunday and  ascade are the common examples of program file viruses.

            Worms
             orms are the computer programs or algorithms which are alien to the host computer and are designed to
            purposely slow down the functioning of a computer.  orms replicate inside the system and thus occupy a huge
            memory space in the storage device.  orms spread more commonly in computers that are connected to a
            network.  xamples of worms are  inux  allpit  Morris worm      Nimda worm  Mydoom  Sasser  etc.

            Trojan Horse
             ro ans are infectious programs which silently infect the computer and corrupt the files of a host computer.
            Such programs often accompany computer games but unlike worms they don t replicate themselves.  hey
            are activated when the user is busy interacting with the entertaining programs or with interface like computer
            games. Some examples of  ro an are  inux   ifatch  Infostealer.  ronbank  etc.

             ro an  orses are often used by hackers as they can enter into the database of a computer system under the
            guise of some entertaining package.  he term  backdoor  is often used for tro an horse.  he user interacts
            with the program and simultaneously the infection takes place behind the interactive interface. Once a tro an
            horse has infected a computer system  it becomes easier for a hacker to access it remotely and perform
            unethical operations and steal important information from the infected computer.

             o prevent a  ro an  orse virus from entering and infecting a computer  it is advisable not to open spams
            email attachments or files that may look attractive and luring but have been sent by unknown senders on the
            Internet.


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