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    The different types of malware include virus, worms, trojan horse, spyware, zombies, ransomware,
                     rootkits and backdoors.

                          Virus

                     A computer virus is a ‘piece of code’ or program developed to corrupt the data or program files stored
                     on the computer system. It enters in the computer without permission of the user. The user may
                     not even realise that the computer is affected by a virus. Viruses typically infect just one computer,
                     however, if the computer is a part of a network, then the computer virus may spread to other systems

                     much like a human virus which transmits from one person to another.

                          Worms

                     A computer worm is a type of malware that can replicate itself without any human interaction. It
                     consumes lots of memory space in replication. Once a computer has been infected by a worm, its

                     processing speed gets slowdown, works unexpectedly and halts other tasks. A computer worm can
                     spread itself from one computer to the other by replication process.

                          Trojan Horse

                     The purpose of a trojan horse is to conceal itself inside the software that seems legitimate. When the

                     software is installed on the system, the trojan activates and infects the host system.

                                                                 Tech Fact
                          The term ‘trojan’ is derived from the Trojan Horse story in Greek mythology, which explains
                          how the Greeks were able to enter the fortified city of Troy by hiding their soldiers in a large
                         wooden horse given to the Trojans as a gift. The Trojans were very fond of horses and trusted
                              the gift blindly. In the night, the soldiers emerged and attacked the city from within.

                          Spyware

                     The primary function of spyware is to monitor a user’s activity and send back the information it gathers
                     to a hacker. Spyware does not have any infection mechanisms of its own. It is usually dropped by
                     trojans (and also by viruses and worms). Once dropped, it installs itself on the victim’s computer and

                     remains there silently to avoid detection.

                          Zombie

                       A zombie works similarly to spyware. Although the infection mechanisms remain the same, a zombie
                     does not usually collect information from the computer. Instead, it just sits there waiting for commands

                     from the hacker. Hackers can sometimes infect hundreds of thousands of computers, turning them
                     into zombie machines.

                                                                                          Computer Safety and Security  71

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