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CLASS 7, CHAPTER 7: COMPUTER VIRUSES, , 1. Fill in the blanks., a. Latin, d. Macro, , b. boot records, e. worm, , 2. Circle the correct option., a. (iii), b. (i), , c. (i), , c. malicious, software, f. Virus definitions, , d. (iii), , e. (i), , f., , (iii), , 3. Give two examples of each of the following destructive programs., a. Acid Rain, Sunday, b. Sircam, CodeRed, c. Polyboot.B, Stoned virus, d. WM_Concept.A, Melissa, e. Back Orifice, SubSeven, f. Frodo, Joshi, 4. Put a tick () for the correct statements and a cross () for the wrong ones., a., , , , b., , , , c., , , , d., , , , e., , , , f., , , , 5. Answer the questions., a. A computer virus is a software program that is designed to interrupt the normal operation of a, computer and make the computer perform undesired actions. It has the ability to make copies, of (replicate) itself and to attach itself to other files or programs., The full form of VIRUS is Vital Information Resources Under Siege., b. Worms often use networks such as the Internet to spread from one computer system to, another. They do not require any human action to spread. For example, a typical worm uses the, address book of the infected computer to spread further. It e-mails copies of itself to everyone, listed in the address book to infect their computers., c. Three symptoms that indicate virus infection are given below.,  Menus and dialog boxes appear distorted.,  The computer operates slower than usual or restarts on its own.,  There can be more files on the hard disk than it earlier had., d. Five harmful effects caused by viruses are listed below.,  They corrupt executable program files such as word processors, operating system, etc.,  They delete information from files.,  They increase the size of files by attaching themselves to those files.,  They monitor activity and steal important data such as credit card information, account, number and password.,  They format the hard disk, thus destroying the data., e. (i) Boot sector virus, This virus infects the boot sector of a hard disk, floppy disk or pen drive. The boot sector of a, disk contains the start-up instructions, which are required to load the operating system in, the computer memory. The boot sector virus overwrites the original boot record with the

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infected one. When other disks are used on the infected computer, the virus is transferred, to their boot sectors also., (ii) Stealth virus, This virus attempts to hide its presence using simple techniques, such as hiding the change, in date and time or hiding the increase in file size. Some even prevent antivirus software, from reading the part of the file where the virus is located., (iii) Macro virus, This virus infects data files. These viruses attach themselves to a word processing or a, spreadsheet file (typically a Word or Excel file) as a macro. A macro is a saved sequence of, commands which can be played back with a single command or a keyboard stroke. When an, infected document or spreadsheet file is opened, it replaces one of the standard macros, with the infected version, which can then infect all the subsequent documents. It also, spreads to other computers on transferring infected documents to those computers., (iv) Spyware, It is a type of malware that is installed on computers and gathers information about the, users without their knowledge. They secretly monitor the users’ activities and collect, information such as their net surfing habits, types of websites they visit, etc. They then pass, this information to advertisers or other interesting parties. Sometimes, they also change, certain computer settings which makes the computer slow and difficult to work with., f. Two common ways through which viruses can spread from one computer to another are as, follows.,  Viruses can enter the system when the system is booted with an infected pen drive, CD or, DVD.,  An e-mail attachment has become one of the common sources of spreading viruses. When, an e-mail attachment containing a virus is opened, the virus enters the computer., g. Malware refers to any program that enters into a computer and causes harm to it without the, user’s knowledge. It is a general term for all destructive programs, including computer viruses,, worms, Trojan horses, spyware and other unwanted programs., h. Antivirus software are the application programs designed to detect, prevent and remove viruses, from the computer systems. They scan all the files and folders of the computer system to look, for the viruses listed in its database of viruses called virus definitions. As new viruses are being, developed and released all the time, it is important to update this database regularly. If the virus, definitions are not updated, the antivirus program will not be able to prevent newly discovered, viruses from infecting your computer system., i. In case of virus detection, the antivirus software performs one of the following actions.,  It removes the virus and repairs the infected file.,  It deletes both the virus and the infected file.,  If it detects an unknown virus, it quarantines (isolates) the infected file. Such a file is stored, in a special area called Quarantine. Files that are in Quarantine cannot interact with the rest, of the system., 6. Application-based questions., a. (i) Multipartite virus, (ii) Ghostball, Invader, b. (i) Antivirus software, (ii) Quick Heal Total Security, McAfee VirusScan and AVG Antivirus